I was about to propose the same thing for the i62HD some days ago, but as I haven't ordered mine yet, I thought I was being a bit overenthusiastic. So I'm glad you said it!
To generate the manual I would vote for the wiki, as it is very easy and quick to edite it.
I think it would be very nice to have a sticky post for each model (i62 and M92) with the main information. It could be the one for the firmware updates, but adding a link to the wiki pages: for the M92 and  for the i62 (maybe update it with the information of the i62HD? or create a new page?). And then each wiki page should link to the manual, which as you said could be created as a shared effort between users.
I think this would both be helpful for the current Boox owners and also for those who are considering buying one.