@votan: If it is true that you have to change every single file for something like the column width, it might really require some change in structure. But you also have to ask yourself how often a change like this really happens.
I will look into this once I had time to read the code of LibAddonMenu. I only saw bits and pieces until now so I can't really comment on it yet.
And yes. We let the library be a library and if we really want extra themes and saved vars and stuff, we put that into a separate addon which will augment the library.
What I actually wanted to say is, I just created the project on github:
https://github.com/sirinsidiator/ESO-LibAddonMenu
Don't mind the eclipse project files and build directory. If you are interested in how to use them, I can write about it in a separate thread.