I'm probably not the first person to think of this but it is something I just thought up on my own the other day while listening to a hip hop song (can't remember which though!).
Emily Dickinson's prolific and ingenious use of slant rhyme could be considered a forerunner to modern day hip hop. Think of how constricted hip hop lyrics would be if they didn't take advantage of the slant rhyme? And who is more responsible for bringing it into lyrical consciousness more than Emily Dickinson?
Oh dammit. Look at that. I just googled "slant rhyme hip hop" and the first hit is a lesson plan on teaching rhyme and slant rhyme involving Nas and Emily Dickinson! I knew I couldn't have been the first one to think this, but I truly swear I thought it up on my own. I love this lesson plan, too. in fact the whole website is neat-o: