Call me dull, but why don't you just build an android app and buy a Fire Tablet to power your project.

A Fire Tablet is probably on par for power and is fully integrated with a touch screen and battery, and with discounts it costs almost or cheaper than a bare Pi.

I feel like we bend over backwards to try to use the Raspberry Pi to do cool things, but a lot of these projects can be developed more easily and powered by a more consistent framework using a Fire Tablet.