Put whatever switches you want on it and it can be!

On a more serious note, that’s a really cool project!

As it happens, I spent quite a bit of time last night learning about the qmk firmware and was looking around for a “keyboard development board”…

Do you think that you’d aim to grow the firmware to support bigger boards?

For me personally, no. But I think the threeboard firmware is small enough right now that it's very readable and understandable, so it could make a good starting point to fork and adapt to different boards!