In terms of nerfs, here's where I'm leaning.
ORIGINS
Cultist - 3 Cultist is a little too strong. If you get an early Chosen Cultist you can clean up the early game. I'm iffy on nerfing 9 though, you need Chosen and a few high cost units to get there. It should still be rewarding.
Elderwood - Almost feel like it's a certainty to get hit I think, although there's a chance that they nerf individual units like Nunu and Ashe instead.
Spirit - It's being seen quite a bit right now. Guessing 4 Spirit will get toned down.
CLASSES
Brawler - They might tweak down the 6/8 Brawler bonuses. It's a little nuts right now, although there are other contributing factors like Elderwood and Sett.
Shade - May or may not get touched. The fact that Zed and Evelynn are both so individually strong contributes to Shade feeling a tad overtuned.
CHAMPS
Ahri - Probably going to get nerfed, though personally I think Guardian Angel is the problem but I think they'll be reluctant to change that.
Ashe - Pretty busted right now. She got over buffed and I'm pretty confident they'll bring her back down.
Nunu - Wouldn't be surprised if his ability gets nerfed, even on top of an Elderwood nerf. The damage increase is just crazy.
Riven - Not sure there's any doubt she's getting nerfed. Probably the best carry in the game right now with the right items/synergy.
Sett - Crazy strong but also a 5 cost so maybe they just leave him.
Zed - Pretty busted with the right items. Dominates early and mid game and doesn't even really fall off all that much if he has the right items.
In terms of buffs, I think some good candidate are Divine, 6 Fortune, Mage (especially 3), Azir, Ezreal, Kayn, and Xin Zhao.