6 year is a bare minimum life as high end console for this gen, unless the producer followed Nintendo's way: initial investments wouldn't be recovered otherwise, or, in the best case, net total life profits would be so small to give a very little justification to billion $ investments. If they plan to kill XB360 short after XB720 release, instead of following Sony's way to keep the old console as entry-level offer, they'll likely need an at least 7 year lifespan for XB720.
Obviously, if MS' main goal is to harm Sony and not profiting too, this doesn't apply, but I have some doubts, Sony itself prevented PS3 from being the danger MS feared, as too little RAM makes it not viable as home/living room computer, right now MS should fear more Nintendo, and the tactics it used against Sony are already proven ineffective against the current market leader.







