Toward a "modern" Emacs

RMS said

> It would create a different editor that we Emacs users would never switch to.

And, I'd say, yes, that's still probably the best way forward. I don't think doing it multiple times as you suggest is a good idea, because it is a lot of work to maintain multiple defaults and all have them all work well. There are people are doing it already https://www.emacswiki.org/emacs/StarterKits. I suspect a good way forward for modernizing emacs is for one of those projects to make a concerted effort to get merged upstream and maintain the code in upstream.