ok just saw the comment mentioning oembed .. yes I can see that could make a quite big difference for a lot of people, especially facebook/twiitter/etc users used to pasting a link and seeng it turn into a video or some other embedded content from somewhere else.

probably hard to add its a ui/rendering option that has nothing to do with whether messages are delivered via xmpp or irc or any other protocol .. those are separate requests for hints about how to render something .. probably http/json - can be done clientside

some users might what to choose which sites use oembed and which just show a link there - so maybe some extra user settings too

I'd be very surprised if oembed hasn't already turned up somewhere in the xmpp wiorld though ...