I think Janssen could turn into a decent allrounder, he's looked handy with the bat and if his bowling continues to impress the way it has so far, he'll be a fixture in the team for the next 15 years. At least South Africa aren't likely to fall into the English trap of focusing all their attention on his batting to the detriment of his bowling.
I have also been impressed with Petersen, van der Dussen and Bavuma and the way they've grown in confidence through the series. In the first test, South Africa looked in trouble as soon as Elgar got out, 2nd test he hung around while they started to back him up, this test they took up the baton very well.