I really hope Universal steps up and goes ahead with "At The Mountains..." I'd be incredibly pissed off if they don't. However, the good news is the possibility of del Toro, Cameron and co. taking it to another studio. If they can take it to Fox, without them dicking around with it, then by all means go for it.
Pacific Rim sounds cool and all(even kind of Lovecraftian, being how the creatures presumably come from the water. And Cthulhu DOES sleep deep under the Pacific...), but it's not what I want del Toro to tackle. He's said numerous times that he doesn't want to do a rebound film. Hopefully, he won't have to.
And thinking about it, it's even more disappointing that Universal is hesitant, considering they were the studio responsible for the first boom in American horror cinema back in the 30's. They took a huge chance with Dracula in 1931, and despite the eventual huge drop in budget in order to get it made, they still took a gamble and perhaps would have closed shop had the film tanked.
It's time to be ballsy with horror again, Universal. Go for it.