The hobby is driven mainly by crotchety old white males, so the likelihood of a rap pin is probably never going to catch.
Look at your poll... The majority of people not only hate the music, but everything about it (I don't even want them to expand because it's probably toxic).
Rap isn't the garbage you hear in the mainstream now. It's the golden era (early 90s) suck as Rakim, Tribe Called Quest, Souls of Mischief, Gangstar, Wu-Tand, Nas, Mobb Deep, etc.
A Wu-Tand pin would probably be the most successful of that era due to it's ongoing popularity, relevance in hip hop, and the fact it's a very marketable brand.
Plus, there is a plethora of ideas that translate right into pinball. 36 Chambers wizard mode, spelling M-E-T-H-O-D or C.R.E.A.M on the stand ups, call outs like "protect ya neck" as your ball save, and more...
But hey, why do something this awesome when we can just release another rock pin that allows guys to relive a time in college where they weren't getting laid