UPDATE!
Eta Prime posted a teardown video of the at@games Sega Genesis Flashback HD. Great news: It runs android. I think we all suspected as much, but it's nice to know for sure.

The hardware is a rockchip rk3036. Specs for that chip indicate a Dual-Core Cortex A7 "up to 1.26 GHz" (we don't know yet if it's actually clocked that fast or slower), a Mali-400MP GPU, and DDR3 RAM (Probably 2GB). There is an accessible micro-USB port inside the case. Good hardware altogether, plus we have that cartridge slot, the two 9-pin controller ports, and the Genesis-style case.
Now we just need to replace the terri-bad software. Since this box runs android, we can assume it's only a matter of time until someone hacks it. Huzzah! This hardware with better software would be the best Genesis HD Clone Console.
Link to the original video for reference: