This sounds awesome, best part is that it's Weekly :) So this means one week I could do a concept art piece, next week a monster, next week a environment piece. Sounds like fun !
I think the main thing is just to spark an idea. You can do whatever you want, be it a sculpt, a sketch, a full on painting, a model. It's upto you how much you put in and how far you go with it. It's not like the speed sculpts where you do your hour and that's it, you put in what you wanna get out. Some people like me…
I'd be up for a bit of weekly sculpting, but the thing that always refrains me from joining this kind of jam or a competition is that the themes are often focused on mutants, monsters and geek nostalgia, and that's just not my area of interest. I like the idea, but it'll depend on the individual topic whether I'll join in…