When neovim does something new and cool that I want to use, then ex-mode-in-vim will obviously not support that new and cool something. If neovim continues to provide an ex mode, then it will be available to me.

Obviously, whether this makes sense depends on what the something is - if it's some GUI flourish, then it's irrelevant either way, but a GUI flourish is not going to be why I move to neovim in the first place.