I think it's safe to say that at this point, if you have not received an acceptance or rejection, you are effectively on the waitlist. Stay strong, it's going to be a long ride. This late in the game, I would guess that the waitlist will move as acceptances are acted upon (confirmed or declined). When I received my acceptance on 3/26, I was given a hard deadline of April 10 (2 weeks) for submission of my enrollment agreement. The adcom has also continually stated that they meet at least once weekly to go over who has submitted EAs, who has declined or failed to communicate their intent to matriculate, who has withdrawn applications, etc and reevaluate the waitlist file by file.
I would not be surprised if nothing went out between now and Mid-May (3ish weeks after the April interview date). I would also not be surprised if they sent out a few more acceptances on April 10-11-12-13.
I believe if you backread, someone posted the format of the day. It is a modified MMI format with both scenario and traditional interview elements, so this late in the cycle, I would expect most applicants to be both familiar with and ready for the actual interview.