Two possible outcomes I see:
1) After a bit of whining everyone will settle and just continue on the old path. This is the more likely version.
2) Creators will start finding other platforms, they will be scattered around, to different ones and most viewers will lose the convenience, of finding everything from the same source. Creators will lose lots of viewers, at least in the beginning, who will oppose the new platforms.
Meanwhile I, a beginner with nothing to lose, will grab my popcorn, and see where it all goes.
Edit: Are you sure the thumbnails will go? Because I can use custom thumbnails, and I can not monetize my videos yet.