There's no way to implement an 1/8" audio jack. I mean, cell phone manufacturers are dropping them because they are too thick... and we are thinner than any other cell phone on the market. The external dimensions of most jacks are close to the same thickness as our entire device.
It may well be possible to implement the audio through the USB, so you could use an adapter there.
I'm also looking at ways to have some female pin connectors on the edge of the device, but it looks difficult.
Better quality sound with some hardware volume control is something I would love to do. I feel we are on the edge of getting some quality sound libraries (@JO3RI) so this would be really nice. We should be able to fit an actual speaker, but then we will need an amplifier circuit. So things get complicated and expensive quickly. But we are looking at it.
Large Internal Memory:
This is of course ideal, but any chip that starts to have significant memory (megabytes) typically is physically large with a package of high pin count (larger than the qfn44 we use now) and/or also is just way overpowered in terms of absolute pin count, processor speed, power consumption, and cost of the processor.
What would be ideal, would be a chip that allows for external code execution but that doesn't start happening until ARM6/7 which puts us in the territory of heavier power consumption. And as others have note if we put a chip of that horsepower in the device, we are competing with actual gameboy hardware. But maybe it makes sense way down the line once we get a color screen which wont be for a year or two.
Right now looking at the SAM21D, it would give us compatibility with the Arduino Zero, it's got more memory and faster than our current chip and it's actually cheaper than what we are currently using.
Seeed, our manufacturer and distributor, actually just put a NRF52 module in their store:
Going to mess around with this a little bit.