I could even imagine such a system having two different CPUs (or, more likely, different cpu performance cores in a single package) that power up/down based on wired power availability, basically just automatically getting many times faster when connected to power and not having to conserve juice on battery. Storage and memory are already fairly low power these days, and tiny. Mobile (i.e. handheld) GPUs are now powerful/efficient enough to run high-res handheld displays with all day battery life, which while probably not 4k gaming level, are more than enough to run a multimonitor desktop setup when not gaming, especially if you make the quite safe assumption that they'll have wall power to crank up the GPU whenever asked to run external displays.
I'm really excited about mobile computing over the next ten years. The Nintendo Switch and M1 iPad Pro are little glimpses into this future. I look forward to replacing the dozen computers in my lab with a single handheld device that can simultaneously virtualize many of them and conveniently multiplex several big displays between them, and come with me in my pocket when I leave.