The more I think about this, the more I think this is mostly due to pressure from the industry side of things. I have a hard time thinking there's a real clamor for completely new hardware every 3 years, especially if it's just a spec jump. But there's several upsides for developers on this one:
Iterative consoles, as Phil Spencer said earlier this year, means no longer having to do significant groundwork in developing for a new platform. If the platform remains the same and it's the specs that change, that makes things easier. No longer do we have developers trying to pressure Sony/MS into putting specific specs and then subsequently being disappointed that he machines are weaker than they thought. No longer do Sony/MS need to do the entire "new platform" song and dance and try to convince gamers to hop on their platform as well as developers to make games for it. Consoles are also pretty risky since if you fuck up the launch of your console, it takes YEARS before you can get a do-over. I know MS really wants a do-over right about now.
Unfortunately none of this has much to do with the consumer (except obviously companies doing well on the business side of things means better products for the consumer). They're still asking people to spend hundreds after about 3 years (if the PS4K launches this year) to play the latest and greatest, and if this keeps happening there's no real telling how many iterations can keep a console before you need to upgrade. Plus, if they keep doing iterations in one continuous never-ending cycle, how do you drum up interest? Because new console generations also means new controllers, new hardware design, new sleek UIs, that's enough to get people excited. That's another thing they need to convince people about.
