Despite the intense awesomeness that would be a StarCraft MMOFPS, I'd have to agree with Sixis and say that's probably not going to happen.
But at the same time if this "fact" that Blizzard is releasing a StarCraft MMOG turns out to be just that, a fact, then I'd hope Blizzard wouldn't just re-release WoW with a StarCraft theme. And the way they could do something different would be to make an MMOFPS.
But who knows, maybe they look at this as the sequel to WoW.
"Coming in 3 years a new WoW with better graphics, improvements and a whole new setting: StarCraft!"
Ugh now that I've typed it, it sounds like that's probably the truth of it.