If we do implement themes here in L4W, I like the idea of custom themes for the L4W setting.
It gives another option to characters for connecting themselves to the setting, many already do this via backgrounds.
If we could find a way to "generic" the themes like the way we did backgrounds, limiting their power, but broadening their fluff. That would be best.
That way any of the older characters could craft a theme around what they have already been doing, and new characters could craft a theme toward what they want to be doing.
The trouble with that, as I understand so far, is that themes are much more broad in their mechanical options than "+2 to skill, make a class skill, learn a language".
Maybe something like, no more than 2w, cannot daze, so on...
I don't have a clear concept for this yet, but the idea there.