The problem with the UI was the it was done in a rush, without much thought of it being moddable. So basically to make it moddable, they need to redo it, which would involve a lot of man-hours.
Imho atm we can live with the UI, like it or not. It may grow on you or it may not, but in the end, what we need are proper FUNCTIONS, not looks. A different less Windows 8/Tablet look would be nice, but there are more pressing issues on the table.
As for the textures, they're a moddable using 3rd party utils, such as Asset Explorer. I've already posted examples of a modified weapon DDS (texture) file that works fine ingame. Making new 3d assets is more complicated and will require a Unity Pro license to create a new asset package, but already we have people who own such license and who would be ready to help packaging the items if needed.
The main issues with modding now are:
- updating the JAF map editor (they're probably waiting to finish all post-release patching in order to do that)
- re-enabling Steam Workshop
- re-externalising sound files (they're waiting on Unity to fix their shit with memleaks)
- more guides on advanced modding (such as programming scripted "scenes" to be used for story telling)