AFAICT, ex-mode is usually used for scripting, as an alternative to sed, awk, and/or perl.
So even if you have neovim set up as your "vi", you'll probably still have an "ex" available on your command line. It'll just be symlinked to legacy vim, not neovim.
The post doesn't make it clear at first, but they're not removing support for reading ex commands from stdin, just the interactive ex mode you can enter from inside the editor.
So even if you have neovim set up as your "vi", you'll probably still have an "ex" available on your command line. It'll just be symlinked to legacy vim, not neovim.