I think MS like they did with the first XBox is going to bail on this generation cycle. They can't win it.
XBox 2 in fall 2017, full upgrade from XB1, 10 TFLOP processor (14nm) + 16GB HBM2 RAM, 2K-4K resolution support, 4K Blu-Ray, upgradable system, runs full Windows.
2017 is a bit early but I expect a new Xbox fall 2018, launching the new gen a year earlier than Sony again. Also don't expect a 10TFLOP console next year for 399 or 499, too soon. MS can ride it out with the Xbone until 2018, it still has some life left in it unlike the Wii U.
If Xbox 2 is 2017 it might not have as many meaningful upgrades compared to launching later. Multiplats will still be made around the 5-6GB ram limits of Gen 8 and looking at Microsofts output in the first 2 years of the Xbone's life, I don't expect the exclusives that do push the hardware make the graphical differences.
If MS is pushing themselves in that situation, then PS4K will be fine, both consoles would be seen as an extension of the current gen even if MS meant to start a new one. It's in MS's best interest to stay close to Sony and not start disrupting the market, they're in a very weak position to change anything. Sony wouldn't be pushed to release the PS5.
PS5 would come in 2019 or 2020, launching with true next gen hardware, +10TFLOP, 10nm, 32GB HBM3 RAM, native 4K
With full 3rd party support. Hype going through the roof.
Xbox 2 would be like what the Dreamcast was to PS2 hardware wise. The DC launched 18 months ahead of the PS2.
Dreamcast had 16MB ram, PS2 had 32MB