Both Sony and Ms ,picked the platform for many reasons but one of them was definitely the fact that not only does it it give them BC going forward it does it a way that's a lot cheaper than the old model, and I remember Sony saying console cycles may be nearer to 5 years then 7 years , this had to do with the fact that less R&D and quicker timelines stemming from using the same platform.
The same reasons that some say makes it opportune to do inter generational upgrades , the problem is it can also back fire by not giving people enough reason to upgrade and what happens if you have Xbox one then PS4 then Xbox 1.5 in that order power wise , you may end up with the PS4 being the one that becomes the lead platform and where does that leave the xbox 1.5 , on top of that what happens if in say 12 to 18 months later having done it's cycle , you get a even stronger PS5 billed as the real next gen , also you have to take into account Nintendo in all this , so you could end up with a confusing mess.