I think it's a great idea and something of a challenge. I do a very similar thing to challenge myself already (go somewhere with one camera/lens and one roll of film). Printing 12 frames in a month is probably not possible for me as I have an 11 month old here (I've been in the darkroom 3 times this year).
However, if there was, say, a bunch of threads each titled with a lens length (35mm, 50mm, 85mm, etc) and then people could 'drop-in' so to speak whenever they've completed their 12 frames, that may attract more interest.
OK, thanks for that Perkeleelinen. I didn't think about the printing aspect, which is a fair enough suggestion - maybe run it over a similar timeframe such as the postcard type exchanges.