Maybe...just because they went APU route this generation doesn't mean they can't revert to older model.
As for 1070 level...that is way, way too weak to be called next gen.
I don't know if I'd say way too weak, but definitely kind of weak. Vega 56 is roughly equivalent to a 1070, and Vega 56 is 8 tflops compared to 1.8 for PS4, so a bit more than 4x more powerful than PS4. The main problem I see with it is that 8 tflops is only 25% better XB1 X, sure it wouldn't be handicapped by a weak CPU like XB1 X is, but still. MS could just wait until 2020 and release a new APU based Xbox that is around 9 tflops for $500 and sell it alongside the older XB1 X at $250-300, able to play 9th gen games at 1080p vs 4K on the new 9th gen Xbox.