Kakoune too. But if a project focuses on a novel editing model and not some other aspect of an editor, then implementing it inside Emacs might be the best approach.

If implemented inside Emacs, then it composes with the rest of its package ecosystem. Kakoune, Helix, etc. are somewhat set back by having to reproduce functionality equivalent to Magit, Org, LSP mode, and so on in order to be on equal footing for many users.

Evil, Meow, and God mode seem to show that Emacs is a good platform for such experimentation.