A lot of modern smartphones and tablets have HDMI output, so you can carry them around in your pocket and plug them in to a big screen plus a bluetooth keyboard and mouse. Of course, then you're stuck with a somewhat underpowered device with a UI that's designed for a 5" screen and doesn't scale well to a larger display.
That said, I'd love for someone to resurrect the Samsung research project from about 10 years ago that did partial migration with Xen. They had a demo where they ran a VM on a phone, then plugged it into a big computer and used the OS hotplug facilities to make it think that it now had more cores, more RAM, and some extra peripherals, in a NUMA arrangement: memory pages were automatically faulted across between the machines by the hypervisor and if the scheduler moved a process to the fast CPUs it would eventually move over. The only real problem was that everything broke horribly if you unplugged the phone before migrating everything back, but that could be solved by providing a dock that doesn't release the phone until it's either powered off or everything is migrated back. This arrangement let you use a small mobile device for everyday computing, but move large workloads transparently to more powerful compute resources when you needed them.