Thinking "Clearly" About 4K

The real advantage of this console "upgrade cycle" is that now a developer should be able to produce a good 1080p @ 60 Hz game without loosing pixel quality.

However what is likely going to happen instead is 1st party titles under 4K marketing pressure will try for 4K, accepting a reduction of pixel quality, and get stuck at 30Hz. Games built around 30Hz won't scale to 60Hz due to CPU loads, etc, and we don't get 60Hz this round in the general case. Instead games will generally offer some amount of extra super-sampling for 1080p on upgrade consoles.

Beating the System
If I was developing a console game for the "upgrade generation", I'd take advantage of 4K by dropping render resolution to 960x540 (yeah) in the game, then use a stylized CRT up-sampler. The advantage of 4K: 540p shader scaled to 2160p has 4 lines per rendered line, so it is possible to have the scan-line effect without loosing as much brightness (three mostly solid lines with one 50% darker gap line is only a 1/8 drop in total brightness). 540p@60Hz on a PS4 Pro is 135 Kflop/pixel, or roughly a 4.6x scaling of perf/pixel from a 1080p@30Hz PS4 title. That would be a transformative visual upgrade.

Maths

CONCLUSIONS ON 4K FOR CONSOLE "UPGRADE CYCLE"
=============================================

Majority of devs will render way under 4K,
adopting up-scaling temporal AA to get to 4K,
and will stay with 30Hz.

The why,

Xbox 360 was a 720p@30Hz target with 9 Kflop/pix.
Many developers did less than 720p rendering on the 360.

Xbox One is a 1080p@30Hz target with 19 Kflop/pix.
So roughly double Xbox 360 perf/pix, a transformative change.
Many developers continue to do less than 1080p rendering on Xbox One.

PS4 is a 1080p@30Hz target with 29 Kflop/pix.
I'm going to take this as the baseline Kflop/pix requirement 
for a current generation visual standard.

PS4 PRO in my opinion is a good 1080p@60Hz target with 34 Kflop/pix,
as that maintains the PS4's perf/pixel standard.
To hit 4K@30Hz is 17 Kflop/pix, 
which is a downgrade to an Xbox One perf/pix level.

Xbox Scorpio, using a 6.0 Tflop number, at 4K@30Hz is 24 Kflop/pix, 
which does *not* hit the PS4 perf/pix quality standard,
but does maintain an Xbox One perf/pix level.
So as with 360 and XB1, devs will continue to render under native resolution.


RAW DATA
========

Using "Google Supplied" numbers for Tflops,

 360 -> .24 Tflops [Xbox 360    ]
 XB1 -> 1.2 Tflops [Xbox One    ]
 PS4 -> 1.8 Tflops [PS4         ]
 PRO -> 4.2 Tflops [PS4 Pro     ]
 SCO -> 6.0 Tflops [Xbox Scorpio]

And looking at flop/pix in units of 1000,

                                    360   XB1   PS4   PRO   SCO
 ================================= ===== ===== ===== ===== =====
  960 x _540 @  30 Hz =  16 Mpix/s   15    77   116   270   386
 1280 x  720 @  30 Hz =  28 Mpix/s    9    43    65   152   217
  960 x  540 @  60 Hz =  31 Mpix/s    8  __39_   58   135   193
 1280 x  720 @  60 Hz =  55 Mpix/s    4    22    33    76   109
  960 x  540 @ 120 Hz =  62 Mpix/s    4    19    29    68    96
 1920 x 1080 @  30 Hz =  62 Mpix/s    4    19  __29_   68    96
 1280 x  720 @ 120 Hz = 111 Mpix/s    2    11    16    38    54
 1920 x 1080 @  60 Hz = 124 Mpix/s    2    10    14  __34_ __48_
 1920 x 1080 @ 120 Hz = 249 Mpix/s    1     5     7    17    24
 3840 x 2160 @  30 Hz = 249 Mpix/s    1     5     7    17    24
 3840 x 2160 @  60 Hz = 498 Mpix/s    0     2     4     8    12
 3840 x 2160 @ 120 Hz = 995 Mpix/s    0     1     2     4     6