The problem is you'd end up with almost the same underutilization in a scenario where the "core" was provided by one device -- for the big desktop setup, for example, you'd still need a large display, power supply, input devices, etc... yeah, you'd be able to lose the powerful CPU (which is sitting idle when not being used anyway), but you'd replace it with (admittedly less complex) support chips that handle the remote-desktop-from-the-smartphone features. How would that be handled? With a low-power SoC. So in almost any situation, it ends up being worth it just to spend a tiny bit more on a good SoC — then you'd have more power, both devices able to be used simultaneously and/or by different people without compromise, etc.
Should be possible with the Connect app thats been out since the Anniversary update
Currently, nearly every device I have is massively underutilized because I'm chained to a fix UI (screen size) for a given moment / need.
p.s. Do you know if this new Surface (via some W10 feature?) will be able to serve as an extended monitor for my laptop. At home I'm used to an extra screen but on the road that's no possible. 10" would be better than nothing.