It might well be decent. But unless some ground breaking new tech is present, it would be a small jump than the one we had when passing from last generation to the current.
720p to 1080p is a 2,25x increase in resolution. 1080p to 4K is a 4x increase in resolution.
If we divide the Gflops/Tflops we had/have by the 720p/1080p, we can get the gain of flops per pixel we had on the generation jump.
To get the exact same jump from the current generation to a next one at 4K we would need more than 26 Tflops (just do the math). This will not be achieved for next generation. It would be too expensive.
But we can get by with a lot less. Using reconstruction tecniques like the PS4 Pro does, we can reduce the Tflops needs to about 13 Tflops.
With these 13 Tflops we could have all current gen games at native 4K, 60 fps (Due also to Zen), and a new generation, with exact the same gains over the current one that we had on the current over the previous, at checkerboard rendering, or other similar tech. Once again this is just math.
10 Tflops would be a gain alright. It would be suficient. But owners of mid generation consoles will shure be disapointed by it. The jump on those cases would be small on the GPU side.
According to
Tweaktown, Navi 10 will be able to reach up to 30 Tflops. This seems to mean that a cheaper and with lower clocks version of it can easily get to about 13.
Without any ground breaking new tech that allows performance gains, thats about the performance I'm betting on.