No, not a discussion, but you’re welcome to! Analysis of the verbosity of famous (or less so) rappers: Link.
No huge surprises, I think but I’ll have to look real hard. And not that lower = worse music, but I like the Jay-Z quote if you scroll all the way down. The second range is the particularly popular stuff. Yes, this means that Insane Clown Posse has a larger vocabulary than 2Pac. Or Kanye, but then there’s only so many synonyms of rhymes for “genius” for him to work with.
Kool Keith, Chuck D and Mr. Lif are, IMO, the rappers with the largest vocabs.
ETA: I looked at the link AFTER I posted, and sure enough, Kool Keith is #2 or #3 on that list, depending on if you wanna count a guy with 1 album. And Aesop Rock has a terrific vocab, but his songs suck for the most part. I declare my man Keith to be the winner! WOOT! 
Without looking at the link, I’d mention Chino XL.
Hmm…he doesn’t seem to have been included in the sample. But Canibus is high on that list, so that’s cool.
Yeah, if you want to guess before clicking.
Couldn’t really get into Aesop but maybe it needed more. I’m pretty sure that Canibus is the only rapper to name check John von Neumann.
Really nice analysis in that link. It’s good he doesn’t use it as an excuse to kick any of the artists (or make fun of rap in general, which I thought might be the reason for the exercise), and he acknowledges the limitations of the data. A+
I’d be curious to see if anyone’s ever done this with poets and prose writers. Large vocabulary vs small vocabulary in creative content doesn’t mean much at all to me, but it is interesting to see it plotted out, data nerd that I am.
Shakespeare I’m sure has had many, many. For more contemporary: Hunger Games vs. Twilight vs. Harry Potter.
It’s like Sabermetrics for literature. Not sure what to think of it. (Well, that’s a lie. I do know what to think of it. But, still, interesting on a data nerd sort of level.)