While it can’t exactly replace the entire UI, this is the entire point of my project EveVision.
It’s a EULA-legal way to extend the EVE Online UI. It’s only a little over a month old and is currently mostly a way to use existing third party tools ingame, but I’m already working on the real goal - a plugin system for others to develop beautiful EVE-themed UI components just like in WoW that can be used without fear of it infecting your computer or sending off your character’s data somewhere. All you have to know is HTML, CSS, and TypeScript. Someone already reimplemented the original Jukebox themselves within a week of EveVision’s release, and now it’s part of EveVision.