Anyone else curious who these other 2 unnamed partners are? I'd laugh if one was Sony... but then again, the PS3 and 360 share a similar code base with PowerPC, so it wouldn't be out of the question for the next gen to again share similar processors for devs to work with. And look at the Vita - it is quad core ARM based. Developing for Vita and PS4 will be easier that way. See a trend here? Heck, maybe the other silent partner is Nintendo. After all, the 3DS (and subesquet DS systems) are ARM based.
I can see it using a Windows 8 core. After all, Windows 8 is being designed to homogenize all platforms with a common OS and user interface, from mobiles, tablets, laptops, and desktops.
And if that's the case, maybe they will be trying something like a hybrid console/handheld, in which case the ARM processor is proven as an efficient chipset in this area.
Nintendo fired the first shots with Wii U. I'm curious how the others respond.