I'm a huge Halo fan and am really excited for this, but was very surprised. I was expecting Halo 4 to headline the next Xbox. While yes, there is a chance they will announce a new Xbox, I think they will wait until 2014 or 2015.
So, at this point I'm looking for Halo 5 to headline the new Xbox and they will use Halo 4 as a proving grounds for 343 Industries. Which in the end is perfectly fine with me.