If you refer to credits, then you should know that everyone that did a minimal contribution once (a single line of translation, or a single bug report, etc.) but disappeared afterward count as "contributor".
More realistically, and from my own point of view, ETL team looks more like half of a developer, overworking, unpaid, and that usually has to deal with a considerable amount of crap from the community. Not referring to TM, but to the community as a whole in general.
Don't get the wrong idea: long term maintenance of this project is a constant struggle. It's working out so far, but current situation is far from being ideal.
Of course, anyone is welcome to join and to help!
Edit: And to answer your question about AC: Bystry is right. Being open source means implementing a traditional AC is near impossible, as it would be very easy to bypass by cheat creator. Not even taking into account our small size as a team, there is indeed very little room for manoeuver.