Hey @deudice, you can see how the waitlist works here:
http://talk.qa.collegeconfidential.com/discussion/comment/22691230/#Comment_22691230
The waitlist process is pretty organized and already set in stone in terms of procedure (it’s a ranked waitlist, but they no longer tell students where they are on that waitlist for each applicant pool), so I don’t think a letter of interest will change any of that, but you could always try and send it anyways.