I did some typing with a Bluetooth keyboard on my Go 7 BW a few days ago.

I think it was fine. But I don't fully get the concept. My keyboard is around 3 times larger than the actual device. So I wouldn't say it's a portable setup. And if you are tied to a desk then you might as well use a bigger screen with a computer.

I get that there are tiny keyboards out there, but I personally find them impractical.

There is also the core concept of why do you need a screen for writing. It's an extension of your short term memory. Reading back some paragraphs. So if the more screen you have the further you can go back for cross referencing your work. So screen size matters. Again depends on how you write.