Some thoughts about the shifts, the suspect & the future meta :
Kecleon looks terrific. Protean is an insane ability for a mon which has a large movepool. It's pretty hard to play around with it thanks to its natural good special bulk and stuff like Drain Punch or even Recover on other sets. It doesn't have a lot of safe switch-ins either, STAB on every move makes it good against everything and it has enough priority to surprise the opponent with the typing. Toxic stall is always an option but there aren't a lot of mon able to stall it. Otherwise, it's a nice mon to support the team with SR and a decent frosttom switch in. I wont be surprised if it's suspected during the next weeks.
Before Abomasnow comes in the tier, you need at least one ice checks against frosttom. Now, you need two or three. I don't know yet if the presence of Obamasnow here will be healthy or not but one thing is sure now, it will have a big impact. Scarf, Z-Move, Leftovers, LO,... All these sets can be customisable according to your team and bring something able to improve the pressure against the opponent's team. Abosmanow is now a threat to take into account in your teambuilding, it's an excellent pokemon.
About what we lose, I think this is what will have the bigger impact in the tier. But I wouldn't be too pessimist here. Lose Torterra, Poliwrath, Liepard and Lycanroc will have a major influence for ZU but we can except in a positive way. Rain was overpowered with Liepard + Poliwrath and restricted a lot the teambuilding, once Kabutops get banned (I hope), the playstyle will be less threaten and healtier than it was before the shifts. The presence of Abomasnow nerfs rain too. Liepard was a too strong pursuit trapper as well, stuff like Darkvally or Pawniard can still trap but without have the momentum move, the dumb speed or the movepool which makes it impredictible. Lycanroc restricted a lot the teambuilding too with only 2-3 counters (Torterra, Poli, Pyuku), it would be certainely quickbanned if it stayed in ZU. The dual dance Torterra's set was an issue too in the process of teambuilding, you needed bronzor, rotom-fan or a fat grass types to prevent the huge damages it does to balanced.
Probopass was a wonderful role compresser with its ability to set up rocks in being a switch-in to frosttom, its departure is bad for the tier. Lose Pyuku is hard too, stall needs to focus on ditto, shedistall, Mareanie or wooper meme to work now. Even outside stall, Pyuku was useful for fat balanced to stop set up sweepers such as monferno or M.Mime, I'm sad it left. Don't have Manectric is less an issue, the only impact it will have it's to make other electric types better, especially Zebstrika. We lose the only viable Spinner bar armaldo with Sandslash rising to NU, not a big problem either. Lose Terra and Poliwrath will have as negative impact to increase the power of rock spam and some unhealthy mon like Vigoroth (especially since Lycan rises too), lose a rocker and a phazer (very useful against some set up sweeper like muk), lose a solid role compresser and one of our only fighting types.
So what will change in the meta with all these shifts ?
Frosttom is in a weird situation. We could say it loses a lot with the shifts. Indeed, Frosttom hits SE against a lot of mons which rise, the presence of Abomasnow will increase the number of ice checks in the teams, it gains Kecleon in switch-in, loses some good partners like Liepard and is weak to mons which gain a lot in viability with the shifts. However, the life isn't totally black for Frosttom. Lose Terra and Sandslash is too lose two rockers which blocks its electric Stab, Lycanroc has always been an issue for the fridge, without manectric there is less competition between what electric type choose, it loses too one good switch-in which was also a rocker with the departure of Probopass. To end this, even if the presence of Abomasnow increases the number of ice checks, it offers to frosttom a 100% blizzard precision under hail which is insane and a partener to spam ice moves. So my conclusion is, even it's not intuitive, Frosttom is stronger now than it was before shifts.
Looks barely broken mon. You have Mareanie in your team ? No ? You don't have a single switch in to Monferno so. It loses two of its three switch in with the shifts (Pyuku and Poliwrath), a check with Sandslash, and it is insane against ice checks which are more than mandatory now. Ferno is the mon which beneficts the most about the shifts, fortunately it is slow. It's in my opinion the second best mon in ZU now just after Frosttom. I wont be surprised if it becomes S in the few next weeks.
They are both better (unforunately). Lose Probopass, Pyuku, Poliwrath, Lycanroc, Liepard is a gift of the sky for them. Muk is a frosttom switch-in and Vigo can switch one time too. If ScarfAbo runs Focus blast over Earthquake it cannot pass Muk. Without FB, it cannot deal with Vigo. They look both pretty unhealthy to be honnest. Wait&see, they are maybe more manageable than I think.
Torterra is gone, Poliwrath too, Sandslash as well and we lack of rockers to punish ice types. Welcome back. Spam Stone Edge looks quite stupid now if the opponent doesn't have any steel types. I don't think I've something to add, they will be both very good.
We're fighting types.
Find a mon which can take Abomasnow, which set up rock and which handles the EdgeQuake. Welcome Bronzor. Other steel types like Metang and Mawile are better too but Bronzor looks the best one. Probopass/Liepard gone means too it's more difficult to trap it (except if you run Darkvally/Pawniard). It's a wonderful role compresser to add in a team.
The only Monferno switch-in in ZU. It has Haze to prevents to set up to take the place of Pyuku, Toxic spikes is very useful against any match ups and Regenerator is godlike in a meta where you have to switch a lot. I could see in the future Mareanie climbs until A-/A rank.
Even if they don't have the same roll, they gain both something with the shift. Zebstrika will be the new Manectric now it's gone, it will be far better than it was before (even if it wasn't bad). Without Terra, Electivire is a bit more free, there are less electric types too and the most important is there aren't a lot mons able to switch into now. It is fast in a meta more offensive than never before and is able to break balanced core. Scarf Electivire is too the only scarf electric type which outspeeds frosttom. Good place for both.
Liepard is gone.
Both the best ice switch ins, Grumpig likes a meta without Liepard too. Regice can now even run ice body to take still better Abomasnow, clear body stays a nice option against Vallys.
Have an hail setter is very nice for beartic which could be excellent in hail playstyle now. Lycanroc-Midnight not only lose its big brother, it loses Terra/Poliwrath/Pyuku/Sandslash which stop it for its sweep. Rock types are globally renforced with this new meta. Lycan will have a decent niche now.
EDIT :
Rock type + Magnet Pull user now Probopass is gone. Even if it's a bit less effective than its Partner, that's a solid option. I won't be surprise if it climbs in B during the next weeks.
Fast attackers
Lycanroc and Liepard were an issue for them (and stuff like Terra/poli/pyuku for some). Now, their speed remains excellent for the tier and their usage will probably go up.
Lose in viability
Grass types
Lose Pyuku + Poliwrath (and even Terra) and the introduction of Abomasnow is quite hard for grass types. However, they wont become bad but if before the shifts they were one of the best types of the meta, they wont be at the same level of viability now. They look less useful than they were before (especially to handle Z-Wood Hammer or to pressure stall) and gain a new grass type which hurt them a lot. You don't have specific reason to run one now, they will decline in viability and probably progressively in usage.
Weather (except hail)
Weather playstyle suffer a lot about the shifts. Rain, even if they lose two of their good answers in Poliwrath and Pyuku, lose in the same time Liepard and Poliwrath which were almost mandatory in rain. Kabutops will be probably quicbanned too. The introduction to Abomasnow is terrible to rain which gains a mon hable to take water/electric move, remove the weather and punish them on the switch with a strong blizzard/giga-drain or Wood Hammer. Sand loses all its abusers except duggy-alola, I don't think it can be considering like a viable playstyle now. Sun is certainly the playstyle which loses the less comparing to the others but has unfortunately a lot of grass types inside and Abomasnow is a big issue for weather teams lacking of insta weather setters. Finally, Abomasnow looks terrible for all weather playstyle except obviously hail which is renforced
Stall
Lose Pyuku is a terrible pain for stall. It isn't unplayable and stuff like Ditto stall, shedistall, Mareanie stall or wooper stall stays viable but the lack of pyuku will have an important impact on this playstyle. I've nothing special to add here except if it makes the teambuilding more free, it shows ZU is now a meta very offensive (too much ?). It's not a bad news but not a good one either.
The meta with the tiershift looks globally more offensive than it was before. Ice spam and rock spam are the big winners of this and grass types suffer about that.
About the suspect
Ban Kabutops, I abstain about Ursaring.
I wont write much here because other people explain it already and i'm pretty sure some council members will write a post about that. Kabutops doesn't have any viable switch in the tier except maybe Hakamo-o, at +2 in speed (aka with Swift Swim or Weak Armor) it outspeeds the whole tier and destroys the offensive teams which are the best archetype right now. It's a slower Lycanroc but without counters and with a second stab. Ban it.
I'm not sure about Ursaring because don't have switch-in doesn't mean it's a broken mon. Otherwise, Ursaring will be banned in PU and NU too because it doesn't have a single switch in in these tiers either. The problem with Ursaring is it's better in ZU than in other tiers thanks to Momentum moves like Volt Switch/U-Turn/Parting shot which are all very common with the Vallys and Frosstom/Monferno/Chatot, etc. Activate the flam orb is pretty easy. ZU is globally slower too which helps Ursaring a lot, especially under webs. The meta looks however more offensive now and i've trouble to see it more effective than it was in the past. Ursa invalides too stall but like every wallbreaker does. I don't have a strong opinion about this susbject, I won't miss Ursaring if it leaves but i cannot say if it's broken or not. I abstain.
Obviously, the meta isn't fixed yet so that was only my thoughts and some predictions about what the meta could look with all these changes.
