Looks like Issue 9374 already covers most of this, with fixes in 2.7, 3.2 and 3.3.

$ python3.3
Python 3.3.2 (default, May 16 2013, 23:40:52) 
[GCC 4.6.3] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> from urllib.parse import urlparse
>>> urlparse("protocol://servername:port/")
ParseResult(scheme='protocol', netloc='servername:port', path='/', params='', query='', fragment='')
>>> urlparse("rtmp://a.rtmp.youtube.com/videolive?ns=yt-live&id=123456&itag=35&signature=blahblahblah/yt-live.123456.35")
ParseResult(scheme='rtmp', netloc='a.rtmp.youtube.com', path='/videolive', params='', query='ns=yt-live&id=123456&itag=35&signature=blahblahblah/yt-live.123456.35', fragment='')

Now there are only the three unresolved aspects listed below, as I see it. Personally I think the first, for urljoin(), should be fixed (hopefully in a generic way without whitelists). I mentioned this in Issue 18828. I wonder if last two really matter?

* uses_relative: would allow urljoin() to work. Compare urljoin("rtmp://host/", "path") and urljoin("rtsp://host/", "path").
* uses_netloc: would affect urlunsplit(("rtmp", "", "/path", "", ""))
* uses_params: would affect urlparse("rtmp://host/;a=b")