Personally, I'll only really start modding StarCraft II when Blizzard increases the map dimensions and adds the multiplayer campaign feature, assuming they'll do it for Heart of the Swarm, otherwise I doubt I'll even buy the game unless someone offers me it; I sort of bought (half bought half gift) Wings of Liberty because of the modding offers it promised, I feel rewarded because of the campaign, but as for modding, we're drowned in, first, the legality issues that WherewolfTherewolf mentioned, second, the inability to do anything medieval-related until our artist start developing new stuff, and third, the stupid limitations we've been imposed which I hope Blizzard is planning to undo in future expansions.
Risks, RPs, RPGs, and anything medieval-themed are killed off for the time being, so I doubt those map types are going to be seen until a few years from now.
EDIT: Hmm, this is actually a good thing to rant about in the e-mail Blizzard sent me.