Maybe some kind of chart or plan can be set up in the OP? In previous clubs, I've seen events organized on the OP (such as 'CURRENT CHALLENGE:xxxxxxxxxxxxxxx, lasting until xxx Participants: xxxxxx') that were organized based on the general availability of members. I think about a week of time was given for the participants to do their thing, maybe we can link to some kind of off-site poll to see which option people prefer? Then again, that club was rather small compared to this one, so I'm not sure it'll work.
I think I'd probably give it a little more than a week, considering how finicky the artistic process can be with some people, but I think this is a good idea, actually. Monthly themes, or a current event of the... whenever (monthly? bi-monthly?) to mix it up a bit.
I'm just slow as hell right now because again, depression is kicking my *** like you wouldn't believe, but I am compiling a list of ideas as they strike me.