Jazz is improvisational music over a set rhythm - just like hip-hop! When jazz was at its height, it was much more formulaic and designed for a more mainstream audience - swing - when jazz started to become less popular, the music that was produced in the genre was much more esoteric and experimental. Stuff like this work by John Coltrane or Stan Getz, which sound so complex that only a professor or academic could really appreciate it:
That was Stan Getz, here is some Coltrane:
On "Stardust," Coltrane takes an old swing song and just takes it in one hundred different directions. It's definitely not for the average music listener or the faint of heart.
I think that, as a whole, hip-hop may go in a similar direction. Alot of very bad things came out of hip-hop when it became mainstream - gangsta rap was not a productive or fruitful mode of expression and hurt alot of people. The genre as a whole, however, is still viable and I think that people like ?uestlove, Madlib, Mos Def and others represent the jazz core at the center of hip-hop.
Our own Kenan Bell is definitely in the jazz ancestry as well - his music often takes samples not particularly known for hip-hop and moves them in new directions. He has sampled the soundtrack for the Watchmen as well as Neil Young, very different samples than the standard 1970s soul samples most rappers like. Music like his may not end up having the audience that Tupac, B.I.G. or Eminem got in their heyday, sure but it may sound alot smarter and leave a better mark on music.