I'm really excited to see what kinds of fun GameFreak will make out of the bag of old tricks. Pokémon is stuffed with "gimmicks" used by only one or two 'mons, or moves and abilities with poor distribution. Stuff that could use some more time in the limelight. Here's an incomplete list of things I wish GameFreak will distribute again:
Sketch - Let's face it, Sketch is the single best move a Pokémon could have in its movepool. It's so good that it would break any non-Smeargle Pokémon able to learn it. If a Pokémon were given a single chance to learn any move it desires, it would sure create a bunch of interesting options. However, for it not to be broken, it would have to be restricted to one use only (so that you couldn't go Heart Scaling your way to filling your four moveslots of whatever). Single-use Sketch tutor à la FRLG, for instance? Or treating it like Rotom-A's special attack, meaning that you could only learn Sketch again if you traded away the previously Sketched move? This would certainly be fun to play with. It looks like an awesome idea on Necturna, at least.
No Guard - Machamp and Golurk both make good use of this, but as far as Pokémon go, they are pretty similar and do many of the same things with their unique ability (that is, DynamicPunch and not a lot more). Perhaps it could be given to a special attacker or a status inducer? (and no, I refuse to count Karrablast)
Flower Gift - Awesome ability, terrible user. Imagine Shaymin, Meganium or even Roserade walking around with this. Neither of them are powerful Physical abusers, but their teammates would send the enemy running for their counter-weather user.
Illusion - Is that Zoroark you're fighting, or that other completely different 'mon you saw in Team Preview? Or is it even an Illusing Pokémon at all? What if it is the original? Multiple Illusion users would almost make Team Preview useless.
Transform - For those times you want to turn the tables on your opponent. It is an extra trick to keep up your sleeve. The enemy took out your Garchomp, and now his own is wreaking your team? Now you have one in reserve! Struggling to beat your opponent's Dragon or Ghost sweeper? Here you have one on your own! It would require careful playing to work well, but the ability to swap one of your Pokémon for something completely different would be incredibly cool. Mew can already pull of this (that's not saying it does), but apart from it or Ditto, no Pokémon have been given a chance to try this cool toy since 1996.
Volt Tacke - there are only three Physical Electric moves with a Base Power greater than 100. Two of them are Bolt Strike and Fusion Bolt, both of which used exclusively by powerful Legendary Pokémon. The third would fit many, many Electric Pokémon flavour-wise, but is instead given to the Pikachu evolution line (which doesn't even use it most of the time). Electivire would appreciate this move. Luxray would. Manectric would. But no, those greedy little rodents keep that move to themselves. Assholes.
Fiery Dance - Another dance move, and (as far as I'm aware) the only exclusive one. It would be to Fire types what Charge Beam is to Electric types, only better. Imagine this in the hands of Infernape or Moltres (Infernape not so much since the move description explicitly mentions wings). Surely a boon worth giving to other 'mons than Volcarona?
Meteor Mash - Too awesome a move to restrict to only two fully evolved Pokémon (three if you count an event Deoxys from some time ago). It wouldn't make that much of a difference for most users, but would perhaps see some use as a coverage move. While the 85% accuracy does hurt, the random Attack boosts certainly help.
Slow Start - Whaaaaat?!? No, really, I'd like to see this again, preferrably in the hands of a more competent user. A decent wall able to hold its own for five turns, forcing the enemy to sacrifice his strategy to force the user out before hell is unleashed. Any user of the ability would by necessity have monstrous stats, but hopefully it wouldn't also have to struggle with Regigigas' movepool. Baton Pass Ingrain and Iron Defense to this monster, and watch the horror on your foe's face as the turn counter dauntlessly creeps towards five.
Some of these wishes might seem like mindless dreaming, but I have to point out that Drizzle and Drought were once exclusive abilities only given to cover legendaries. The list of
signature abilities contains a LOT of asterisks, where previously exclusive abilities have been handed to other users over the years. Stuff like Speed Boost, Rain Dish, Shadow Tag or Magic Guard have spread beyond their "gimmicky" use before. I hope it will happen again.