Very nice work! Especially because it's my favourite form factor - I'm a long-time Preonic user
If you ever offer the final version for sale, you already have a customer
I like the simplicity of the Preonic, but the tray-mount design is pretty dated.
I'm by no means an expert, but I'd like to share some comments if you don't mind. The integrated plate might seem neat, but it's far from a community favourite construction. It's very stiff (especially your version which is
very thick). It also deprives you of plate material choice. If I could make a recommendation - drop the integrated plate and add a few (4 should be enough) mounting points for a removable plate - that way people can use a plate in a material of their choice. For example, polycarbonate, FR4 and POM plates seem to be very popular these days (I've been cutting custom POM plates on my laser-cutter for a while now). If you like an aluminium plate you can still easily mill it separately.
Anyway, I think this board could be pretty popular! 5x12 layout PCBs are not very easy to get off-the shelf, especially in the EU - I'd love to collaborate with you on this project and design one, probably based on the Raspberry Pi RP2040 which is easily available
and very cheap (as opposed to most other MCUs used in custom boards like the good old ATmega32u4 or STM32s). By the way, I run
https://42keebs.eu/, a small family MK shop based in the Czech Republic.
Please let me know what you think
I'll be watching your progress with great interest!