If it's an individual you'd like to interact with further, I'd wait until matriculation to contact him/her, because it will be more relevant once you actually know your workload and schedule.
Also, at the risk of being a terrible downer, you never know if you got admitted in spite of rather than because of what one of the interviewers recommended.
In my life prior to med school, I received several thank you emails from undergrad and job applicants whose admission/employment I did not support. Obviously, I was always professional and polite in response, but it felt awkward and rubbed me the wrong way as a reminder that the respective institution didn't take my feedback seriously.
I would agree that it *can* be a bad idea. My assumption is that the accepted applicant in question (OP) developed a rapport with his interviewers and felt the interview clearly went well. Otherwise, why would they care? Of the three interviewers I have had so far, I connected with two extremely well and I am confident they were big advocates when it came time for committee. The third interviewer and I got along well and I believe it went well, but not to the point where he was actively trying to convince me to come to the school and work with him during the interview itself, which is essentially what happened in the other two interviews.
As a result, I didn't send an email to that third interviewer when I was accepted. I think it goes without saying that you need to use your social skills and figure out who really wants to hear from you, but maybe I shouldn't assume that.
Here's a good guideline if it needs to be spelled out:
If you send your interviewer a thank you email, and didn't get a reply, don't email them again to tell them you were accepted. I mean, come on. Clearly they are very busy, weren't nearly as excited to meet you as you thought, or both.
If you send your interviewer a thank you email, and got several paragraphs in response, I think it's safe to say they don't mind you contacting them to share some good news.
If you didn't send a thank you, why send an email out now?
If you're in some other case, use your judgment based upon past interactions with other
Homo sapiens.