With Natal dropping Fall 2010 and a possible new design for the 360 coming then or after, i doubt you are going to see the next Xbox so soon. They are going to push Natal as the next Xbox 360 experience, i doubt they'll abandon that a yr after its release. We wont even know how successful Natal is for at least a year.
I might be wrong about it, but, unless they are going to start optimizing games for installation, and that is the main reason behind the all USB Storage, because MS wants everyone to have a HDD; or there will an upgraded Xbox coming out in the fall, i say that 2011 will be the begining of the next generation of home consoles (because next gen handhelds is this year).
As for Natal, why do you think that, just because MS might released a new generatiom next year, means that they will abandon it?
Project Natal is an add-on, so, it can very well be hooked to the next Xbox as well.
Gears of War 3 in April makes anyone wonder...
If the Fall is the big season for video games, why take Gears 3 out, when anyone knows that Gears 3 would sell tons on Christimas.
What does MS have in store for Fall 2011.
Halo 4....but, imo, that alone doesn´t cut it.
Besides, the Halo franchise is getting overexposed as it is, so, unless they counterbalance it with a new generation, and Halo 4 being a launch title, i see people getting sick of Halo.
Halo 4 as a launch title would be a massive hit for Microsoft, it would sell millions of the new console in a few months.
Imagine the return of Master Chief and Cortana, with graphics that would make God of War 3 be so last gen, and with the gameplay fans know and love....it would be massive.
IMO, Halo 4 as a launch title for the next Xbox is a certainty, so, the question that remains is, will MS give one-year hiatus to the Halo franchise and only release the next gen in 2012; or will it see the light of day in 2011?
So, unless MS pulls a rabbit out of it´s hat this year (no, Project Natal doesn´t cut it, unless is the best thing ever seen); they have to release the next Xbox next year.