Xbox Scorpio without Zen, but rather an old Jaguar CPU is just not future proof
"Future proof" is a phrase that should never be applied to technology without a serious dose of sarcasm. Some products remain useful longer than others, but any successor is by definition going to have appealing aspects the earlier product lacks.
so you have to buy the next Xbox 3 years down the road, again.
You never have to buy a new a product, but they're going to do their damnedest to make it appealing. They also have limited incentive to extend the life of a product they've already sold you.