The "brand new IP" is in relation to Blizzard, not Capcom so all these suggestions for Capcom games are perfectly valid candidates.

The question I have is why are they announcing them now and not at E3, is it because they are due out incredibly soon and waiting until E3 means less time to promote them or are they simply worried they would get over shadowed come the event. They already have enough games to talk about at PAX so adding two more seems strange.

They've previously said not to expect any Mega Man games at this event but maybe times have changed - like others have said, a compliation rather than a new game would be more likely at this time. I think something like Street Fighter V is too big for an event like this and would better suit either an E3 or even an EVO Finals reveal but I think it's still too soon for SFV, regardless of how much I would like to see it. And since Darkstalkers hasn't been put out to test the waters, I wouldn't expect it to be DS4 either. It could be a HD/online version of Street Fighter Alpha 3 as it's something they touched upon in the last Capcom survey.

My guess is that one of them is Viewtiful Joe HD... for no other reason than me wanting to see another VJ and that I think they'd go that route before dropping a brand new game in the series, especially with the production staff now no longer at Capcom. The thought of VJ in HD or on the 3DS excites me greatly.

So yeah, HDing of old games rather than brand new would be my guesses. Strider perhaps another potential title?