Bump
So after RBG's passing and Biden likely to be elected, I'm changing my prediction to one seat to fill. In the 2021-25, Biden will, in all likelyhood, only pick a replacement for Stephen Breyer. I don't see another seat opening up unless someone dies unexpectedly from collapsing health or an accident. Thomas is just 72, and he I think he's the kind of dude who sticks as long until a GOP prez can name his successor. He may retire in the next term if Trump is reelected. Alito is just turning 70 this year, so he could go for another decade. Roberts, at 65, isn't retiring soon either.
Roberts has also had health issues, although it's unclear how serious they are. This being said, the most likely scenario to my mind is Biden picks Breyers replacement and maybe gets Thomas or Roberts if something unfortunate happens.
So in the next ~4 years probably one appointment maybe two.
It would be strategically smart for McConnell to let Biden replace Breyer with a similar moderate liberal, but that’s the only SCOTUS appointment Biden is getting unless both the Georgia senate seats flip.