I can't imagine that they would want to prolong the life of the original XBox with all the push to the 360. All they would be doing is producing obsolete hardware that would sell at lower and lower prices, instead of making money with the new one (they supposedly make $70 this time?) I can't imagine a market for multiple versions of a current technology as there seemed to be for the PS1 or PS2.
I guess now most versions are out at the beginning of the cycle, with some add-ons (HD-DVD) and major software upgrades possible.