@Rosalind I can relate to that. Even presents and family things aside, I've got some midterms and presentations coming up on top of the usual coursework and parttime work, so I'm in the middle of some pre-Christmas madness myself.
Asking for one post a week is reasonable, no question there. With so many people stating that they are still in it, I really think it's not a lack of interest that's the problem - some don't have the time, others just don't know what to do or if what they have in mind is enough to justify a post.
That being said, I think it may not be unreasonable if everybody who's able posts whenever they can to keep this thing active. With you only getting a chance to post once or twice a week, I don't think you moving the story along whenever you can is too overwhelming. And even if it was, I think that's a small price to pay for keeping the RP as a whole lively.