OK, so I had a look at some ideas for the skills tree, and although it's not my biggest concern within the game personally, I thought I could come up with an idea to make it better, providing a mod of this nature would be possible -
http://smg.photobucket.com/albums/v476/sane_man/?action=view¤t=ImprovedSkillScreen01.jpg
Oh, that is
nice. I can immediately imagine how it's supposed to behave, even before reading your text description. Keeps all the information right there, gives obvious mouse-navigation, and it keeps the impressive swishing-and-zooming of the constellations.
Pair this with an input overhaul for the in-constellation navigation (movement locked to the connecting lines), and it would be perfect.
...A UI mockup should not make me feel this much joy. It's a sign of how bad the existing UI is that just the
thought of using this instead gives me a warm, happy feeling deep in my chest.

Aside, this should totally be possible. Because the UI is coded in Flash it's a pain to reverse-engineer, but it does mean that we can create entirely arbitrary modifications or even entirely new menu interface designs. The only limitations are what data the underlying game engine exposes for use in the Flash menus, and which Flash files the keybindings are hardcoded to bring up (e.g., magic versus inventory menus). However, the SKSE ("script extender") will eventually be able to expose more data to the UI and be able to change how keybindings are mapped to menus. In the end, we should be able to
entirely dispose of the existing interface if modders want to go that route. The existing system is going to be a pain to start modding, but once we get the technical knowledge to do it, the sky's the limit!