The more interesting part of this is that we've come to the end of disruptive console generations. Whatever is the next console from Sony, whether it's called PS4k or PS5, it's going to also be based on FreeBSD, the x86 architecture and use the same PSN infrastructure. It's not going to be like earlier in this generation, where for example Destiny PS4 and Destiny PS3 existed separately from each other, and demanded significant development resources, different servers, and different purchases from the consumer.
Given that we've reached that point in services, software and hardware architecture on the console side, things like cross play between generations are a given. Or cross buy: why make two different discs for two different platforms when it's the exact same code running, just at different graphical presets?
And once you got to that point, why only make bigger jumps every 5 years when you can seamlessly make a jump every 3 years? And by seamlessly, I mean: it would be more expensive to build the original APU from 2013 in 2017 than to make a faster, better APU for cheaper. Why artificially build slower hardware then?
The fears that as soon as a new box comes out the current one is invalidated are not without merit, as that's exactly how the current transition worked out. But the situation is clearly different here, we've reached a new level in technology where things can evolve. Sony and Microsoft would do well to communicate that fact by keeping and actively promoting both the new and old platforms as one. For example, releasing a brand new slim PS4 and PS4k simultaneously at price points like $299 and $449, with the same product branding and all, would send a clear message that they're not dropping an old platform to support a new one.