Vim has actually long had Scheme integration (in the form of plt-scheme and then racket). So you could actually script vim in Scheme. The problem is that virtually no one ever does.
Last I checked, almost all vim scripts were written in vimscript (with Python starting to make some headway). If any non-vimscript language is going to be the future of vim scripting, it's probably going to be python rather than Lisp or Scheme. So if you were going to start writing Scheme scripts in vim, you'd be pretty much the only one.
Compare that to emacs, where virtually the entire gigantic emacs ecosystem is written in Elisp. It's an Elisp ecosystem and community you'd be participating in were you to write in Elisp for emacs. Leveraging that enormous codebase and community is a huge win for emacs that you're not going to get in vim unless you program in vimscript or maybe to some extent in python.
So if you're interested in vimscript or maybe python, vim seems like a good choice, while those interested in Elisp or maybe Scheme would probably be much better off in emacs.
As for Lua, how many vim scripts are written in Lua? I would guess it's about as popular as Scheme is for vim, which is to say virtually not at all. In any case, it's not a Lisp, so I'm not sure how much interest there would be from the Lisp/Scheme communities in programming in it vs something like python, which seems to have more traction in the vim world. It would be a step up from vimscript, though, that's for sure. But, again, there is no Lua ecosystem for vim, so being the only one writing Lua scripts for vim is not hugely attractive for most people.
Just my two cents.