It's been possible to script vim in Lua (and various other languages including Python, Ruby, Perl, and even Scheme) for a long time.. long before neovim existed.

The problem is that the overwhelming majority of vim scripts are written in vimscript. So even if you switch to using some other language to script vim, virtually all the rest of the vim ecosystem will still be in vimscript.

Sure, but now, because neovim is guaranteed to have lua available (not necessarily the case in all vim builds), you can count on it, which in turn eases the problem of consuming the scripts.

Not the same. At least pre vim 8. I don't know if this has changed.

https://geoff.greer.fm/2015/01/15/why-neovim-is-better-than-...

Example for python from the post

  import vim

  # Show current directory in Vim
  cwd = vim.eval('getcwd()')
  vim.command(':Explore %s | redraw' % cwd)

Technically it's python, but it's a shim.

Who is that a problem for?