They didn't want to call the XB360 the XB2 and have it on the shelves next to the PS3 because it would be numerically inferior. So they matched the PS3 number and rationalised the choice with some additional digits and some totally unexplainable reasoning as to why 360. Full circle? Yeah, right! We're not back at Pong, we ain't gone full circle!
I know this, I said as much in my first post
Though my lifestyle suggestions are very tongue-in-cheek, I do think they'll go that route. They'll be looking at Wii and seeing how much sense that makes from a broader audience POV. Shed the ties of a limited brand-name, the existing fans of whom will already know that the new machine is the next XB iteration, and come up with something hip and more inclusive to attract a broader demographic. Just as they did with their OS brand.
I'm not completely sold on shedding the XB brand altogether, but your reasoning is sound.