(or did you mean the ereader? Not tried, sorry)
I found this[0] but it is in Spanish, and many of the links to source don't go anywhere. It seems like they us Debian and Qt, which would be very neat.
[0]: http://www.mibqyyo.com/actualidad/2013/07/10/programa-de-des...
That links to an English version of the page you found: http://www.mibqyyo.com/actualidad/2014/01/08/bq-ereaders-dev...
Note that I don't have the device so I don't know if this works, but if there are problems with the instructions I assume BQ would help (since the open sourceness is a selling point).
The specs of that particular one show no bluetooth (and no OTG usb), so can't connect a keyboard.
It also has no wireless apart from wifi; and only 512MB (though that's plenty for ssh!)
Also, difficult schmifficult! I bet ed, the standard editor, will work just fine. Shouldn't be much worse than, say, a 300 baud terminal!
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).
[0] http://www.engadget.com/2012/02/23/hack-enables-fast-refresh...