Not so sure automatic BC is a thing. There's be tons of little hardware bugaboos maybe. Things to do with millions of variables like CPU cache, let alone the biggie of ESRAM. It will probably be far easier for Sony to have BC next gen by far because they didn't do ESRAM, so I expect they may, but I see MS forgoing it again.
If you abstract away from the hardware too far then you lose what makes consoles, consoles.
Anyways, if what you say is true then I think the next Xbox upgrade/new console imo may come in 4-5 years instead of 3? Who cares what we call it...
It's not just hardware though, a new console gen is almost a total reboot, the dash etc. Look at Xbox to Xbox 360. And then Xbox 360 to Xbox One. Huge changes and improvements in both cases. An incremental model would necessarily see a lot less of that as there just isn't time to do a massive reboot every 2-3 years. So you'd just get the same OS and features mostly, on new, but only incrementally so, hardware.
I dont like the idea. It's just not consoles.
The problem is you just doom Xbox One owners to a subpar experience. If that happens 2-3 years after you paid $500 for a box, bridges are gonna be burned with consumders, and rightfully so.
Speaking to the topic title and offering an alternative then, I think MS has to cut the costs a lot, try to get to $299, try to be "good enough" graphically, continue to pump out games, etc. Try to keep One above 360 sales, at least, then you can at least argue it's some progress.