Bluetooth is an interesting option - we’ve avoided it so far mostly because it’s another step to go wrong when people are building them, but you’re right that it ought to work. It also makes a lot of sense if you use an ESP32 board with onboard bluetooth.
Sangaboard v4 is a hat with 3.3v communication, so once it’s working I suspect some group buys of this will be very helpful. If we can get a CE mark, OFI or Kitspace will definitely try to sell these in the UK, and we’ll do our best to figure out something for other markets if we can - but CE marking will likely take a little while after we have our first batch of working boards… It’s all surface-mount components, so I don’t recommend trying to solder it yourself! Once we have specced it out with a board house, though, I’ll let you know so you can order some even if we aren’t yet set up to sell them.
Given that the two USB ports in question are not on the same side of the microscope, the “rigid cables” probably don’t work. Perhaps a compromise would be right-angled connectors, and then you can run the wire through the Sangaboard “bucket” which wouldn’t be perfect but ought to be neater than your current solution. I’ve not double checked that link, but it gives an idea of what I mean.