I've stated a lot of this before:
IMHO I think the Arduboy is such a success because it didn't strive to be the ultimate portable gaming platform. One main appeal was the challenge of coming up with decent games given the simplicity of the product. Another was the large code and support base provided by being Arduino compatible.
Although there have been some desires for color, communication for multiplayer, and other enhancements, these things start to get away from the goal of being an easy, fun, basic thing for beginners to learn with and to test the abilities of seasoned programmers without much effort.
To me, two main complaints are the limited code and RAM space available, and only allowing one game to be resident at a time. To some extent, the lack of speed may be a minor factor.
With that in mind, if it were me, for the next "Arduboy" I'd just try replacing the ATmega32U4 processor with an ATSAMD21G18 and add a MicroSD slot. Keep the display, buttons, case, battery and most other things identical to the current Arduboy. This would mean:
- Flash increase from 32K to 256K
- RAM increase from 2.5K to 32K
- Clock speed from 16MHz to 48MHz
- (However, none of the above will be precisely comparable, since we're going from an 8 bit AVR architecture to a 32 bit ARM Cortex M0+, but still a big improvement)
- The processor would probably drop in fairly easily, although a small 3.3V regulator would likely have to be added.
- The total cost difference from the current Arduboy would probably be minimal
- The processor is the same one used by the Arduino Zero so the goal would be to make it appear as an Arduino Zero (much like the current Arduboy is a Leonardo). We would still be under the Arduino environment so there wouldn't be much of a learning curve for developers and porting the Arduboy Library and other aspects would likely be quite painless. Many sketches would probably port over with minimal effort.
- The processor has a true DAC built in, which could be wired to the speaker for improved sound capability
- With maybe a little extra circuitry it's possible to run USB in Host mode, meaning one unit in host mode could connect via a cable directly to another unit in device mode for two player capability.
- Battery life would be similar to the current Arduboy
- Hopefully, the case would only require minor modifications to expose the MicroSD slot on one edge
- Since the processor runs at 3.3V, it would interface to the display in a safer manner.
- The time to develop and release this new product would be relatively short compared to other more elaborate proposals
To get an idea of what might be required to use the ATSAMD21G18 and be closely Arduino Zero compatible, the Rabid Prototypes Neutrino is a good example.