Hi everyone
I am also on the waitlist at SIPA and received the same email from Matt Clemons last week. I have asked to remain on the waitlist though I have an offer outstanding from another school (SAIS) for which I have to pay a holding deposit by the end of the week. I agree with your analysis of the waitlist above, and think it is therefore impossible to have any feel for the probability of being accepted now. All in all, v frustrating!
Good luck with it.