This is, after all, the next logical step in the arc of his career as a right-wing demagogue anyway. His schtick has always been about "pushing the envelope," and the social envelope already has been pushed about as far as it can be without descending into overt fascism these part 10 years or more -- thanks to Limbaugh.The Neanderthal Right has always had bug up its butt over Left Wing group think.
Maybe we can call this the New Racism: emerging from behind a mask of genteel conservatism, it openly calls for a revival of ole-time white supremacism, having found that the "liberal social experiment" with racial equality has failed.
Whether it's environmentalism, compassion for the poor, or civil rights, the far right has always chosen rugged individualism over anything that smacks of a shared ethic, unless the ethic originated on the right (abortion, homophobia, Christian values, etc.)
Limbaugh's racist jibes are just an extension of the right's "rugged invidualism" mantra, where persons are freed from the shackles of group think and free to make whatever observations they want, no matter how ill informed or shallow.
After all, it's just radio.