I think a very cool use of the “big blue area superimposed over preview” would be alerting users that the exact same link appears elsewhere in the topic.
Say I am in a long topic … and in post #5 someone posted a link to
http://wow.awesome.com/cool, later a different user comes and composes a reply containing
http://wow.awesome.com/cool, odds are this is
- A dupe post
- Somehow strongly related to the post the submitted the original link
So we should simply display this in the blue area
Bob already posted a link to
http://wow.awesome.com/coolin post #5.