One of the selling points of neovim was to make it more easily embedded into other programs.. doesn’t seem like anyones trying to do so from a quick googling though; maybe one day there can be true unification of the holy editors

I suspect this is quite unlikely. A main reason for emacs being good is that it has a good programming language for extensions and good primitives to support it. This is in comparison to eg vimscript (hopelessly bad) and javascript (extremely mediocre). Emacs Lisp has several advantages:

1. Language is more extensible because of macros so dealing with editor state can be hidden.

2. Language is more dynamic with advice and eval-after-load and such is extensions can play well together

3. For all it’s difficulties, having buffer-local variables and dynamic scope seems to make writing extensions easier

As far as I can tell, making Emacs cooperate with neovim would require shoehorning the editor model of one editor into that of the other, likely causing many extensions and expected behaviours to break.

There is, I think, a difference between making a new application that can use neovim for editing some bits and making an old (or, indeed, very old) application switch to using neovim for editing.

NeoVim supports Lua as well.

Could you elaborate on some of the specific features that Evil was missing? Aside from a couple of exceptions, any differences from Vim are considered bugs.

Most of the differences I noticed revolved around automatically changing indentation levels(one of the best ways to get uninstalled) and autocompletion which sometimes didn't work(file name completion) and once it refused to autocomplete a certain string without removing the underscores first.

I'm sure a lot of this can be fixed by changing some configuration options, but I don't see a reason to change the editor just for the sake of it. Emacs is awesome in some ways, but it's not my cup of tea.

There is no reasonable way to emulate always on

    :set virtualedit=all

Picture mode is not reasonable. The cursor must go where I put it and stay there, not move in any direction I did not choose.

spacemacs.