A list of things to improve on the Commodore PET Mini
The audio is quite noisy. This is a well known Raspberry Pi design flaw when using the 3.5mm. jack connector. When audio is playing it becomes much less noticeable, but it's definitely a problem. A workaround would be to take the audio from the HDMI port, but that involves a whole new circuit board to decode the HDMI signal. Another solution would be to use a USB audio card.
Low power warning when using battery
When using the battery power solution plus the audio amplifier, and specially if you plug something else on the Raspberry Pi's USB ports, it seems the recommended MP2636 charger module from DFRobot can't provide juice enough to power the entire setup, and the Raspberry Pi shows a "low power" warning. The whole thing works, but the Raspberry Pi might throttle down CPU cycles in order to adapt to the scarce amperage. A solution would be to use another charging board that is capable to deliver more than the 2.5 amps this one delivers.
Provide a fake screen 3D printed part
For those who prefer to only have a cute model of the Commodore PET Mini without the electronics, it would be great to provide an alternative version of the Monitor frame piece with an opaque plastic display.
A tiny cartridge to load ROMs
Creating a 3D printed cartridge that fits in the Commodore PET Mini USB ports at the back, and is actually a memory stick that looks like a real cartridge. It would be an ideal and extra-cute solution to transfer roms to your PET Mini.
Provide some Commodore PET ROMs
It would be great to provide some Commodore PET ROMs to download from this site, just to provide all the resources to complete the PET in one place. The provided ROMs should be legally downloadable.
A working keyboard
It would be nuts! And quite difficult to implement, as it would need some kind of interfacing board like the Teensy, and a lot of wiring. Maybe creating a custom PCB to solder tiny switches and then 3D printing and gluing individual keys on top of them? In any case, it would involve a redesign at least of the Body shell 3D model, most probably of all of them since it would force us to scale the whole PET up to fit the working keyboard.
A disk drive unit
Wouldn't it be great to have a Commodore 2040 or 3040 disk drive for your PET Mini? We could even make it functional, connecting it to the PET via USB, and making it work like a real disk drive by mounting a couple of SD Card readers that would simulate the disk drives. The SD Cards would have a printed label to make them look like tiny 5.25 inch floppies!
Solved: A higher refresh rate for the screen
The tiny 2,8 inches screen we're using connects to the Raspberry Pi via GPIO using a slow serial communication. This results in low framerates, probably around 10 - 15 fps. The Raspberry Pi is capable of much more, so this is a bottleneck that could be improved, specially if you plan to game in your PET.
This has been solved by increasing the SPI speed on the Raspberry Pi config, check out the Install screen drivers section!