Nvidia recently released the $329 GTX970 that's about 90-100% faster at 1080P than the GPU in PS4 (~R9 270):
http://www.computerbase.de/2014-09/geforce-gtx-980-970-test-sli-nvidia/6/#diagramm-rating-1920-1080-4xaa-16xaf
At the pace GPUs are evolving (2x the performance increase is now every ~3 years), it'll go like this:
1) end of 2013: 2X faster than PS4 with 780Ti $699 (alternatively now 970/R9 290X is nearly 2X faster for $330-370)
2) end of 2016: 2X faster than 780Ti (or 4X faster than PS4)
3) end of 2019: 4X faster than 780Ti (or 8X faster than PS4)
4) end of 2022: 8X faster than 780Ti (or 16X faster than PS4)
Since PS4 came out November 2013, I think with a 7-8 year life, it'll be replaced by about 2021. That bodes really well for PS5/XB2's performance increase and those consoles should be backwards compatible due to the move to x86 with PS4/XB1 :))))
I think the CPU in PS4 will become a bottleneck faster than 5GB of available VRAM or the graphics capabilities. Crytek has shown that if you tap into the Compute Shader potential of Graphics Core Next, you can get amazing results with R9 270X performing more like a GTX770:
Since on average GTX770 is 31% faster than 270X at 1080P in games, but here it's matching the GTX770, it shows that with proper utilization of compute shaders, the GPU in PS4 has a potential for a 30% gain in games (or a better way to think of it is that you can increase your graphical complexity or anti-aliasing load by 30% and maintain the same performance as a GTX770).
The question remains when will developers start taking advantage of the Compute Shaders in the PS4/XB1's GPU? Right now it seems they are not tapping that potential at all unlike what Crytek did with Ryse: Son of Rome on XB1.
