Having used tablets with external keyboards (both integrated into cases and freestanding), as well as laptops, my on-the-go preference would be a flyweight laptop with integrated keyboard and e-ink screen. Low battery consumption, universally-readable screen, real keyboard, Linux, and low distractions.

Onyx BOOX + Bluetooth keyboard + Termux ... gets me some of the way there, but it's not quite the same, and it's cumbersome to set up. I'd avoid Android if I could.

Thing is that a freestanding (and lightweight) display is also quite useful on its own, for reading, and any hybrid design is going to bump weight up a lot, which starts negating comfort of holding that in your hands and reading.

Which is to say I'm validating your design and thinking here. Watching with interest.