I wouldn't put 70s djs as a gen but a precursor. Start at sugar hill, grand master, blow, dmc as one. A/b rap. Rakim, Kane, heavy d, kid n play, top billin as gen 2(braggadocious mc). Nwa begins 3 with Dre era, snoop on west side and nas, tribe, dela soul, and others on east, era of street reporting rap, then Jay z, biggie, Tupac, diddy, busta, Eminem, nelly, outkast as mainstream hip hop reaches peak for gen 4(braggadocious wealth attainment), the decline follows with only heavy hittas and one hit wonders for gen 5 but Wayne dominates, Drake, a lil jay z and nas, snoop, minaj, Kendrick between 5 and gen 6 with trap music slur shit, future, black Beatles, panda incoherent style with all digital sales.
Like other genres, hip hop had it's peak at 4. By the time it reaches gen 8, my guess is that it will sound electro/techno/trip