[rbanffy]

In theory, at least, you could build a cellphone around a GPU with a couple ARM cores thrown in and keep most of the GPU powered down while you are not docked. When you are connected to a decent power supply over USB-C, you could fire up those cores, provided your phone's back is a massive heat sink (a dock can provide the airflow).

It won't beat a 300W monster or accurately predict the future weather for 10 years, but it'd be more than reasonable for casual gaming.

[k__]

My idea was that the system I dock my smartphone into would add display, input and extra compute via TB

[rbanffy]

But why do you want to move the computing power? The hardware is ubiquitous and cheap. It's your data that's unique.