Speaking of multiplayer mods, i don't many will use WFAS. It has a smaller playerbase and the same modding possibilities. Running the mod on both games would split the playerbase, which is a very bad thing for a multiplayer mod.
Singleplayer mods... it doesn't seem too difficult to port them, but i still doubt that many will make effort. After all almost all the WFAS players own warband anyway.
This is of course about total conversion mods. Smaller mods that just tweak/alter/improve native is en entirely different matter.
