Yeah, it has to be "OTG" (on the go), aka "usb host". Seems relatively uncommon.
Beats a line printer! Can relate - I'm ecstatic that (70s era) unix utilities are blazing instant on a phone. I'm sure vim would also work on an e-reader, if you don't need to find the cursor.
I should research this. Working on e-ink/e-paper would be so much better on the eyes - and incredible battery life (they claim 2 months for the Kindle).
Also, difficult schmifficult! I bet ed, the standard editor, will work just fine. Shouldn't be much worse than, say, a 300 baud terminal!