Well, why does it even matter because Xbox 30 is still pretty new, and I doubt that the new one is coming out anytime soon, so I don't think we should worried on what it's going to be called.
It has not even been 2 years since the 360 has come out. Well, has it? I really doubt it and where did you get 4 years from? It's nowhere near that long.
Well, it kind of does because 360 x 2 = 720 so it does make sense, but that's just a really bad and weird name for it, so I doubt that it'll be called the Xbox 720.
1. They havent said yet. (they might not even know yet) 2. The 360 is about 3 years old since it was released in 2005. 3. I agree with Jierarudo, there should be a Xbox portable.