If you follow any discussions around development, it seems the chance of this happening is essentially zero. I feel that they will continue to diverge into completely different editors.
Hard to say, but as it stands, but my view is that that the typical nvim users want Vim as a full-fledged IDE with little effort whereas Vim users still want Vim largely as a text editor. And of course there are already a whole bunch of incompatible differences between them that would only be noticed by the more "power" users I suppose.