All depends on just what we get with next gen consoles. If we end up with 6 Core Ryzen, 12TFLOP Navi, and 16GB GDDR, then there will be no issue at all making a Portable verision. If we end up with something like 12 Core Ryzen, 18TFLOPs Navi, and 32GB GDDR, then it may be a bit more of a stretch. Just depends on how Sony/Microsoft want to flesh out their ecosystems.
I kinda hope we get a Mobile with 6 Core Ryzen, 3 TFLOPs Navi, and 8GB HBM aiming for 720 -1080p. Then a Base console with 6/12/16GDDR shooting for 1440p, and finally a high end model 12/18/32GDDR aiming for 4K.
Again, what about the power draw? Battery tech hasn't improved too much lately, and the breakthroughs that have happened aren't in consumer products yet. It's easy to say "Oh sure, just throw this chip into a Switch 2, 4k 60fps portably," but the reality is far more complicated than that.