Replace compute module with Librem 5 (and terminal with LibremShell), and i have proposed something very similar:
Basically, put your phone into the laptop-shell and use it as a laptop.
The Librem 5 is already designed to be turned into a workstation (convergence), via USB-C.
See Librem 5 overview, scroll down to “The hardware”.
I think that would be the first step. Or, actually the second, after the Librem 5 became reality 
This is much simpler to achieve, as the compute module is (will be) already there, and the shell is mostly just a regular laptop minus mainboard.
After that, on the path to world domination, modularized phone (like Fairphone) and extra-powerful compute-modules could follow. Or the hardware-keyboard for the Librem 5 some are hoping for. Or, how about extending the Librem 5 like the Nintendo Plus phone concept? Just dreaming