I've got an RPi 3 up and running with a 7" touch display powered from the Pi, and a USB dongle for one of those CanaKit wireless KB/mouse combos. This is all running only off of 2A USB power and I was worried that it'd be too much for it, but it seems to handle stress --cpu 4 without browning out. DraStic probably won't draw as much CPU power as that so I'm going to move forward with this for now. I'll check to see if it ends up throttling when running the emulator. I might just go ahead and order a heatsink now to be on the safe side.
My TODO list right now is to finish the input configuration, do a bit of refactoring, get a screen rotation option in, and get it out to testers. It'll still lack some features that might get in later like shaders (particularly custom ones). For those familiar with the Pandora version, it should be roughly to that feature level and with the same UI, plus configurable controls, rotation, and mouse/stick virtual stylus control. My hope is that the controls will make most games at least tolerable when used with a USB gamepad, which I intend to test for (as well as HDMI out). You might need to use a keyboard to set it up the first time, although it's pretty possible the default controller mapping will be enough to let you change the control settings to best fit your actual controller.
Unfortunately, I can't work on it much immediately because I'm really preoccupied with work, and going to be on travel (again, bluh) the next few days. But I should at the very least have the time between Christmas and New Years on leave and completely open, possibly also a few days before. I'm hoping that'll be enough to get this done, since I really want the first version out by 2017.