I really struggle to see a case for keeping Morkel over Rabada after these past few performances.
JP Duminy is a peculiar case. A lot of the motivation for his selection is the fact that he can bowl some good offspinners. Back when AB was keeping, he seemed a great number 7 - an average of 30-35 is still pretty decent for a number 7, and he added a bit of spin to our otherwise-4-pronged bowling attack.
Now though, between QDK cementing his place and Piedt/Harmer being genuine spin-bowling options, there doesn't seem to be space for Duminy. But our selectors will continuously have it at the back of their mind that we don't have any other bowling options in our top 7 (except perhaps Dean Elgar). We've always been an all-rounder heavy nation (Pollock, Kallis, Hall, Klusener, Boje, Peterson etc) so it's scary territory to only have four decent bowlers.
I've often wondered whether we shouldn't be grooming QDK as an opening batsman rather than as a 7-batting keeper. He does have opening experience, and openers are much harder to find than keepers.