Until Bitwarden screws up it's going to be difficult for any fork to get much attention. If they do, that will the moment to launch a fork.

It's Bitwarden's game to lose. Forking is easy enough that there's no great need to pre-emptively fork.

Vaultwarden is a very lean implementation of Bitwarden but if you want to look into an alternative to the Bitwarden ecosystem, I recommend - AliasVault https://github.com/aliasvault/aliasvault - check it out!