People talk as if you couldn't make a third person in WCIII >.<
It depends really, The only reason DOTA is the only custom being plyed right now is becuase it is essentially the best supported, best designed map for WCIII. there are thousands of amazing maps, but because WCIII is so old no one plays them anymore. When SCII gets out, you're gonna see a lot of remakes of some of the classic WCIII and SC maps, and newer ones. Whatever turns out to be the best SCII map will likely dominate like DOTa is a few years from now.