The transition may have happened by now if hip-hop hadn't proven to be so divisive. Even today, while it is popular among many younger, suburban, white listeners, it has nowhere near the crossover appeal that '60s and '70s soul and '70s and early '80s funk had. The gap between somewhat conventionally composed music and what is basically unsophisticated street rhymes set to a beat with bits of sampled music from the past as enhancement is a bridge too far for many, even 30-some years since rap first broke into the popular music mainstream.
Can the two genres ever coexist in a profitable, advertiser-desirable radio format targeting the 40-year-old listener? I have my doubts.