UChicago is rolling for MSTPs. When I interviewed a month and a half ago, about half of their class was filled. This includes the 12 year old MSTP applicant who is definately going there. This does not include one SDNer who was accepted before interviewing, who turned the offer down. I e-mailed to ask my status, as I was told I would hear about a week after I interviewed, but received no response to my e-mail.
I would go to the interview. It is a pretty nice interview and is all expenses paid, so what do you have to lose? I honestly don't think you will be interviewing for the waitlist.