I believe you independently derived a very old, but lurcrative, idea. Kontera started off back in 2003 although I don't recall when they actually got to double-underline links. Viglink has been doing this more subtly as a commercial service since 2009, and AOL actually had a flavor of this built into Instant Messenger. There were also a number of affiliate networks that built this infrastructure to parse the Commission Junction offers database and update their networks with match/near-match products & services.
