The benefit is indirect rather than direct, as in the user benefits from the increased availability of plugins/guis since they would be easier to create. Also vim lacks lots of very simple but essential features of modern code editors simply because it lacks the graphical capabilities to do so (an example would be displaying the documentation of some method you are autocompleting, something which I have never seen in vim and which I actually believe is impossible).

If it makes vim plugins less painful it has a huge benefit for me. I run almost completely vanilla vim in part because the plugin system is so awkward.

You can not see the concrete user benefits of a modernised, cleaned up code base ? Maybe you need to look harder.