Thankfully, it turns out they were wrong! Official confirmation (of a sort) has come. A Blizzard employee who goes by the forum name of Drysc responded to forum posts speculating about the project. He (or she, maybe -- it's like a female Night Elf Hunter; you can never know) said, "it's an unannounced Next-Gen MMO. And that doesn't mean an expansion for World of Warcraft either."
So Drysc confirmed what most of us already suspected. Hey, better than nothing. So ... is it World of Starcraft? Do we want it to be World of Starcraft? Hmm.