Give a real alternative to those instead of the many quarter-implemented GUI shells that are really no better than running Electron, and the switch might be able to happen.
Yes, if vim were unmaintained I would switch, that would be a reason to change. But it's not, or at very least hasn't been, so I haven't, that hasn't been a reason to.
> It's easier to maintain one codebase than to maintain two forks.
Not necessarily; if the two codebases are maintained by groups of people with incompatible ideas about how the code should work and what it should do, then keeping things separate is much easier.
> If development of vim dropped and neovim was nominated as its successor, I'd think most vim users would be just fine.
Agreed; they don't diverge that much from an end-user's perspective.