lol, let me dream!
Speaking about only the GPU, if the screen is 720p then that means the GPU only has to push 921,600 pixels compared to 2,073,600 for 1080p or 8,294,400 for 4K. If the majority of games on the PS4 are native 4K then the GPU on a portable would just have to push 1/9th the amount of pixels compared to the PS5 itself.
Of course then there's the CPU, RAM and whatever other goodness to contend with... but I'll just sit and hope that a die shrink or two might get them closer to making that a reality :)