Choosing between Bitcoin and Bitcoin Cash is a completely different matter. You choose whichever you like, and you can verify yourself that the software follows

Choosing between Bitcoin and Bitcoin Cash is a completely different matter. You choose whichever you like, and you can verify yourself that the software follows those rules. There's no chance that users wouldn't converge into their chosen blockchain, because both forks follow the longest chain in their forks. You assume that the community somehow can agree which chain is the correct one in proof-of-stake. This is not true because there's no longest chain rule. Without an authority, users would never be able to converge into the same chain, after a split has happened.