I wish you luck, but a big piece of advice. Don't prepare, because you really can't.. They will ask you NOTHING about your application, your experiences, your ECs, your grades/MCAT, etc. Also, none of the questions in the MMI required a prior, thorough understanding of health delivery systems, universal healthcare, or anything of that sort. On your interview invite webpage, they have a link to an article about MMI...read it and the sample questions on the webpage and you'll see what I mean. They want your view and opinion on medically and non-medically related situations and they want you to think on the spot, so by nature, you can't prepare for that. As cliche as it sounds, just be relaxed and say what comes to mind.
I doubt a Jan 5 interview is for the waitlist. Last year, I think the people who "interviewed for the waitlist" got their invites in late Feb, early March. From what I heard, they were pretty much the guinea pigs for trying out the MMI format. Not sure how many acceptances they've given out, but I have yet to see Cinci come up on the Rejection or Waitlist thread...