I would question Microsoft's goals for a successor at this point. They seem to really be trying to mesh the PC and Xbox together, and it may mean we'll just see the Xbox equivalent of Steam Machines in the next five or six years. If that happens, the power of other machines will be somewhat irrelevant.
Nintendo exists basically in their own development bubble. They are in an exceptionally weird position in the game market, and nothing about this generation could actually affect the NX. Honestly, calling the NX next gen may be pushing it, since people associate next gen with increased power, and the prevalent rumor is that the NX won't even be as powerful as the PS4. That aside, what Sony does is unlikely to greatly affect Nintendo past making it that much more difficult to win third parties back.
Really though, it's hard to know what to expect from next generation. Nintendo seems to be the only one that we can guess is fairly certain to stay on a more standard console development cycle, whereas Sony and Microsoft are both seriously branching out with their various services associated with their game consoles. One thing that is absolutely certain is that we will never see a huge jump like sixth to seventh generation ever again. We are at the point of near hitting realism in our games even with the power of the PS4. Sure, we can go up to 4k or whatever, but in the end, that isn't a game changer.
The only way I see the next generation going forward is by changing the way we play in a meaningful way. It's why I have high hopes for VR, as I feel it has the capacity to push gaming in a new, necessary direction now that general hardware upgrades are becoming less and less relevant.
Back to the main topic though: will PS4 hold back the next generation? Unlikely.
