This certainly looks interesting, but we won't start tracking a feature if it looks like it will never be supported anywhere.

I cannot find any bugs or discussions about adding this to Chromium or Firefox, and WebKit only has a feature request bug from 2009 that doesn't seem like it is going anywhere. Given that RTSP 2.0 was ready to implement four years ago, and has seen basically no support, I find it hard to believe it will be supported anywhere any time soon.

FWIW, it seems the original RTSP was once supported by Firefox OS.

Strangely, the MDN docs say:

Although the and tags are protocol agnostic, no browser currently supports anything other than HTTP

But a little further down:

The process of using the various protocols is reassuringly familiar if you are used to working with media over HTTP.

For example:

<video src="rtsp://myhost.com/mymedia.format">
  <!-- Fallback here -->
</video>

Suggesting that it is possible?