My understanding was that Neovim's main strength was the fact that it is a fresh rewrite for modern platforms only. Whereas Vim has tons of legacy code in it for all sorts of legacy platforms, which makes it harder for people to contribute code, and makes it harder for the dev team to find and fix bugs, or to add features, etc.
In any case, whatever the outcome of the fork is, this is an interesting experiment :
Will the cleaner code base, using more extensively tests and CI move faster than the legacy one ?
Not accounting the number of people contributing to each project, the logic said it should. It will be interesting to see how long it takes to pay the dividend.