This is a very early days in the project but what the features i would like RISC-VLAD are:

• Display: at least the pixel area of the original GameBoy 160 × 144 pixels, 47 × 43 mm.
• Buttons: that are responsive and comfortable to use.
• Audio: can be DAC or PWM based either is acceptable.
• SDcard: slot for storing extra sprites game code ect.
• Power: Needs to be portable (batteries or can run from USBpower stick)
• Programming: Be able to be programmed without additional hardware (Very important) 

Optional:

• Rechargeable power system onboard.
• Wifi
• BLE
• USB

I have initially selected the GD32VF103RBT6 as the MCU which has a 32bit RISC-V based Processing core. This however may change as other options become available.