If it's World of Starcraft, I along with millions of others will be very disappointed. Someone at work tried to tell me that there are people out there that would play a Starcraft MMOG that aren't playing WoW right now. I said, yeah, maybe there are, but the two (WoW and WoS) can't co-exist very well.
For a WoS to have WoW-like success, it would probably have to draw from WoW's current playerbase. I mean there are a lot of people out there that don't like MMOG's regardless of the universe, and there are a crop of MMOG players that will play anything similar.
WoW would see a drop in the number of players and who is to say that WoS would ever get anywhere close to the number of players that WoW has? MMOG's thrive on big communities.
I think it would be a mistake. It would be a slap in the face to Starcraft fans everywhere, especially the ones in South Korea.
Then again, if they haven't even started working on it, then it might not be a bad idea. WoW will be very aged by the time that a WoS would come out if development on it started the day after the announcement.