I feel there are enough rulings discovered that most of the play for rotation battles is now able to be talked about so...here we go.
(This is not a thread to compair Rotation Battles to other Battle Styles or to dismiss Rotation Battles as a battle type that will not be played)
Rotation Battles Rulings from research thread (will edit in as updates come)
Confirmed Pokémon that are rotated out are not "switched" out; they retain all buffs, status conditions, etc. as if they remained in battle.
Confirmed Rotating a Pokemon out does not removes its buffs\debuffs, ability changes, Leech Seed, etc. (Philip7086, Setsuna)
Confirmed Each Pokemon has their own Protect\Detect\Endure\Wide Guard\Fast Guard counter. It does not reset upon being rotated off the field. (Philip7086, jumpluff)
Confirmed Choice item holders remain locked in their move even after being rotated out. (Philip7086, jumpluff)
Confirmed Pursuit does not "chase down" a Pokemon that has been rotated out, presumably doesn't do double damage either. (0mastar)
Confirmed Natural Cure does not activate upon rotating a Pokemon out. (How about Regenerate?) (Philip7086, Setsuna)
Confirmed Entry hazards (Stealth Rock, Spikes, Toxic Spikes) do not damage Pokemon for rotating around on the grid. They only damage Pokemon who are switched out from inside their Pokeball. (Philip7086, The_Chaser)
Confirmed All abilities that are only triggered upon a Pokemon entering the battle do not activate if said Pokemon is merely rotated in. This includes Intimidate, weather abilities, etc. However, if you switch the Pokemon in from your party, its ability will activate. (Philip7086, Setsuna)
Confirmed The game remembers status counters for Toxic and Sleep. In other words, if you take one turn of Toxic damage (6.25%) then rotate out, the next time you rotate in, you will take increased Toxic damage (12.5%) instead of starting back at 6.25% again. Your Sleep count also gets saved, instead of being reset like it does upon switching out, if you rotate out your total slept turns is still counted. (Philip7086, Setsuna)
Confirmed If a Pokemon's type is changed, it will remain changed even if the Pokemon is rotated out. The only way to get rid of a typing change is to use another move that changes its typing, or withdraw the Pokemon into its Pokeball. (Philip7086, Setsuna)
Confirmed The game remembers each Pokemon's last move before rotating out, and Encore will force said Pokemon to use their last move if they are rotated back into a faster Encore. (Philip7086, Setsuna)
Confirmed The effects of Encore, Taunt, etc. get carried with the Pokemon when they are rotated out. In other words, if you are Taunted and you rotate out, the next time you get rotated in, Taunt will still be in effect. Same with Encore, etc. (Philip7086, Setsuna)
Confirmed Intimidate: Affects only the opposing active Pokemon, not all three opponents on the field, and is only activated once while the Pokemon is on the field. (skarm, Afti)
Confirmed Shadow Tag does not prevent a Pokemon from rotating about, only from withdrawing into a Pokeball. (Philip7086, The_Chaser)
Confirmed The Slow Start counter remains constant for an inactive Pokemon. (Philip7086)
Confirmed Weather abilities do not activate unless the Pokemon is the first active Pokemon on the field or fully switched in (from off the field). Does not activate even if rotated in. (SupremeDirt)
Confirmed Plus, Minus, and Flower Gift do not give their respective boosts when the Pokemon is inactive. Presumably the same applies to Victory Star and the like. (Philip7086, The_Chaser)
Confirmed Moves that target multiple Pokemon such as Earthquake, Surf, and Discharge do not damage any Pokemon except the one Pokemon who is active on your opponent's grid at the time. (Philip7086, The_Chaser)
Confirmed You cannot rotate to a Pokemon and switch it out on the same turn. You can only switch a Pokemon out if it is currently active. (Philip7086, The_Chaser)
Confirmed Other constantly present abilities like Pressure only get announced if you lead with the Pokemon, or switch them in from inside a Pokeball. If you rotate one of these Pokemon in, the game will not announce the ability, but its effect will still be active (you will still lose 2 PP if you attack a Pressure Pokemon, etc.). (Philip7086, Setsuna)
Confirmed Pokemon do not receive status damage while they are inactive. (Philip7086, Setsuna)
Confirmed The active Pokemon cannot Baton Pass\U-turn\Volt Change to an inactive Pokemon on the field, only Pokemon in their Pokeballs. (jumpluff, Philip7086)
Confirmed If both sides rotate at the same time, the side with the faster Pokemon rotates first. (Philip7086, jumpluff)
Tentative It appears to be that the act of Rotating is considered a free action. We tried a few things to damage an opponent before rotating out, but none worked. This includes priority moves like Fake Out, Ice Shard, etc., and Pursuit as well. This has very cool competitive implications, seeing as a Pokemon also cannot be damaged by entry hazards -- you can keep an important Pokemon alive no matter what if you want, until it's the last Pokemon! (Philip7086, Setsuna)
Tentative Rotation occurs before any moves are made. Unknown if there are any exceptions. (Coram_Boy)
Confirmed Rotating a Pokemon out does not removes its buffs\debuffs, ability changes, Leech Seed, etc. (Philip7086, Setsuna)
Confirmed Each Pokemon has their own Protect\Detect\Endure\Wide Guard\Fast Guard counter. It does not reset upon being rotated off the field. (Philip7086, jumpluff)
Confirmed Choice item holders remain locked in their move even after being rotated out. (Philip7086, jumpluff)
Confirmed Pursuit does not "chase down" a Pokemon that has been rotated out, presumably doesn't do double damage either. (0mastar)
Confirmed Natural Cure does not activate upon rotating a Pokemon out. (How about Regenerate?) (Philip7086, Setsuna)
Confirmed Entry hazards (Stealth Rock, Spikes, Toxic Spikes) do not damage Pokemon for rotating around on the grid. They only damage Pokemon who are switched out from inside their Pokeball. (Philip7086, The_Chaser)
Confirmed All abilities that are only triggered upon a Pokemon entering the battle do not activate if said Pokemon is merely rotated in. This includes Intimidate, weather abilities, etc. However, if you switch the Pokemon in from your party, its ability will activate. (Philip7086, Setsuna)
Confirmed The game remembers status counters for Toxic and Sleep. In other words, if you take one turn of Toxic damage (6.25%) then rotate out, the next time you rotate in, you will take increased Toxic damage (12.5%) instead of starting back at 6.25% again. Your Sleep count also gets saved, instead of being reset like it does upon switching out, if you rotate out your total slept turns is still counted. (Philip7086, Setsuna)
Confirmed If a Pokemon's type is changed, it will remain changed even if the Pokemon is rotated out. The only way to get rid of a typing change is to use another move that changes its typing, or withdraw the Pokemon into its Pokeball. (Philip7086, Setsuna)
Confirmed The game remembers each Pokemon's last move before rotating out, and Encore will force said Pokemon to use their last move if they are rotated back into a faster Encore. (Philip7086, Setsuna)
Confirmed The effects of Encore, Taunt, etc. get carried with the Pokemon when they are rotated out. In other words, if you are Taunted and you rotate out, the next time you get rotated in, Taunt will still be in effect. Same with Encore, etc. (Philip7086, Setsuna)
Confirmed Intimidate: Affects only the opposing active Pokemon, not all three opponents on the field, and is only activated once while the Pokemon is on the field. (skarm, Afti)
Confirmed Shadow Tag does not prevent a Pokemon from rotating about, only from withdrawing into a Pokeball. (Philip7086, The_Chaser)
Confirmed The Slow Start counter remains constant for an inactive Pokemon. (Philip7086)
Confirmed Weather abilities do not activate unless the Pokemon is the first active Pokemon on the field or fully switched in (from off the field). Does not activate even if rotated in. (SupremeDirt)
Confirmed Plus, Minus, and Flower Gift do not give their respective boosts when the Pokemon is inactive. Presumably the same applies to Victory Star and the like. (Philip7086, The_Chaser)
Confirmed Moves that target multiple Pokemon such as Earthquake, Surf, and Discharge do not damage any Pokemon except the one Pokemon who is active on your opponent's grid at the time. (Philip7086, The_Chaser)
Confirmed You cannot rotate to a Pokemon and switch it out on the same turn. You can only switch a Pokemon out if it is currently active. (Philip7086, The_Chaser)
Confirmed Other constantly present abilities like Pressure only get announced if you lead with the Pokemon, or switch them in from inside a Pokeball. If you rotate one of these Pokemon in, the game will not announce the ability, but its effect will still be active (you will still lose 2 PP if you attack a Pressure Pokemon, etc.). (Philip7086, Setsuna)
Confirmed Pokemon do not receive status damage while they are inactive. (Philip7086, Setsuna)
Confirmed The active Pokemon cannot Baton Pass\U-turn\Volt Change to an inactive Pokemon on the field, only Pokemon in their Pokeballs. (jumpluff, Philip7086)
Confirmed If both sides rotate at the same time, the side with the faster Pokemon rotates first. (Philip7086, jumpluff)
Tentative It appears to be that the act of Rotating is considered a free action. We tried a few things to damage an opponent before rotating out, but none worked. This includes priority moves like Fake Out, Ice Shard, etc., and Pursuit as well. This has very cool competitive implications, seeing as a Pokemon also cannot be damaged by entry hazards -- you can keep an important Pokemon alive no matter what if you want, until it's the last Pokemon! (Philip7086, Setsuna)
Tentative Rotation occurs before any moves are made. Unknown if there are any exceptions. (Coram_Boy)
Summary: Rotation battles are a new battle type introduced in Generation 5. In these battles you send out three pokemon though only one pokemon is truely considered in play. At the beginning of your turn you select which of your three pokemon you wish to be sent in or switch out your current pokemon for a new middle pokemon (just like in singles). This requires a large amount of prediction and more to think about than simply just a one on one battle.
Strategies to consider when building a team
The 4th Member: You opponent only sees at most 3 pokemon on your team in a rotation battle at any given time. However, there is a fourth person, the one you can switch in. This means that an extremely large deal of thought should go into who is the first pokemon you've sent out and what members may support them. This goes the other way as well since your opponent can do the same. For example, your opponent has a gyarados to start in the center with a scizor and an infernape at the side but they have an eletrivire just in case of electric attacks. Remember that your opponent could switch to someone out on the field of play at any time of the battle when you least expect it and that there are still 3 other people on your opponents team that are not out!
Stat Storing: A pokemon rotated out keeps its stat increases. So storing a pokemon with stat increases for later in a battle probably isn't a bad idea. That way when you need the help you can just send in your +2 DD Ononokusu when you need it the most.
These are only two things to consider! Discuss the Rotation Battle strategies and play!