I looked through the issues, but this doesn't seem to have been suggested before. So... would this be possible?

Worked on signs once before and lost my work. In the end, there's so many great sign mods out there the ability to simply cover a sign seems so insignificant compared to what other mods can do.

This would be great! I really am tired of looking at the default signs.

I think I've seen it suggested before and the comment was that the GUI problem was holding the idea back.

For what it's worth, I love the idea and want it badly :)

I'm just too lazy to do the GUI stuff, but the sign itself isn't terribly hard to implement.