They're all going to have quite divergent opinions on how to structure the fork and various other design decisions that would inevitably lead to forks of the fork again.

I think forking VS Code is probably the most sensible strategy and I think that will remain the case for many years. Really, I don't think it's changing until AI agents get so ridiculously good that you can vibe code an entire full-featured polished editor in one or a few sessions with an LLM. Then we'll be seeing lots of de novo editors.