It's April 16th today, most applicants should have made their final decision for graduate school. However, earlier this year, I was interviewed by a very prestigious university in the US for their ECE PhD program. In February, I was notified that I'm on their waitlist. Now the resolution deadline has passed, but I still haven't received their final decision on my application. I wonder am I still supposed to receive one, or if this is a rejection? Is it appropriate for me to send an email to the professor who interviewed me if they're still considering my application? Thanks!
No this is not a rejection.
Let's think about how admissions works.
The department has a certain number of spots. They send out offers to some number of people (which might be more than the number of spots if they are sufficiently confident that some people with decline). If people decline their offers and they still have spots left, then they send out offers to people on the waitlist.
April 15th is the final reply deadline, so there are some people who declined their offers today. Sending out new offers isn't instantaneous, so you can expect some offers to be sent out well into next week. Some of those offers will get declined as well, with more new offers being sent because of that. Sometimes people are offered admission and or funding well into the summer.
However, if you are on the waitlist, it is reasonable to send a brief e-mail saying that you are still interested. On the flipside, if you accept a different offer, it would also be polite to proactively send an e-mail letting them know you are not interested in staying on the waitlist.