I used to have the MD be turned off at night (at around 2am).
But it took the MD too long to power-on so I just leave it running. One other thing that can't work is the turning on of the pipes after power-on.
For example, atm, when the MD is powered off, and you say: Play TV, the MD will get powered on, but as the DCERouter is stateless, the Play TV never will reach its recipient. So what happens is: The MD will turn on. Full stop. Nothing more. That is not nice. And there is no easy way around this atm, due to the mentioned stateless-ness.
So, all in all, nice idea, but not doable with LinuxMCE without some MAJOR rewrite of the internals.