There a lively discussion going on in other regions of the Open Anthropology Cooperative (what a terrific name, by the way) about the sustainability of this initiative. In my experience with those rare scholarly groups that achieve this elusive goal, e.g. Savage Minds, the Association of Internet Researchers (AoIR), or the EASA Media Anthropology Network, the key is to have a committed hard core of people driving the project, preferably with a good mix of backgrounds (nationality, gender, seniority, etc.), but ensuring as wide and sustained participation as possible over time.
With these thoughts in mind, I'd like to propose an OAC Seminar Series that would give the entire Cooperative a regular online gathering place (say 3 or 4 times a year) and contribute towards its sustainability. We would need to invite people to submit working papers of general anthropological interest and then discuss them online over an allocated period of time, e.g. two weeks. For an example of how this can work in practice, see the Media Anthropology Network site
where you'll find PDF transcripts of dozens of previous e-seminars.