The prototype cases were built out of wood boxes I purchased from Michael's (pictures coming). The power on/off support is handled with a SPDT switch that is tied directly to the power input on two different devices for both the Media Server and Media Player.
In the Media Server the UUGear 7-port hub was unable to power the RPi, so I tied the SPDT directly to the power input on both boards (the UUGear is jumpered to be self-powered only). Ground is common to both devices and the input power (a 5V/4A barrel connected wall-wart).
In the Media Player the SPDT power is tied to the power input on the RPi. The power input comes from a micro USB 5V/2A wall wart that is tied directly to the pico projector. In this way, whenever power is plugged into this box it will try to charge the projector, but will only power the RPi when the SPDT is switched on.
In both cases it's important to have enough amps in the wall-wart/power source or the circuit fails to boot the RPi.
It's a really simple circuit in both cases, using off-the-shelf breakout boards from Sparkfun.
Note that the LiPo power in these prototype cases is just an externally connected Jackery Giant battery pack. But a wall-wart works as well.