I believe that the most authoritative info is still an old post from Gert:
Yes, it can go down in resolution. We are still working in how the user can define these parameters. Probably a (text) configuration file on the SD-card. The same holds for the composite video output. It can do PAL-BGHID, PAL-M, PAL-N, NTSC, NTSC_J. It just a matter of programming the TV-out hardware. We might not support all standards from the beginning though.
My gut feeling is that how to get an usable programmable environment in 480i/576i is something that will be worked out by the community in the coming months.
In my opinion, the most pressing question right now is if out of the box the console output in NTSC/PAL mode will take care of the overscan. IIRC, on the standard linux console you can select the font and limit the number of columns/rows to be displayed, but you cannot set an offset for the topmost/leftmost character. Maybe GNU screen could be an option, but my experience with it is very limited.
I think your right. The agreed resolution was 40 x 24 as matched with the Acorn mode 7.