This seems very much like the core team they would play in the WC:-
1 Hendricks *
2 De Kock'
3 Van der Dussen
4 Du Plessis
5 Miller
6 Mulder *
7 Pretorius *
8 Rabada
9 Nortje *
10 Tahir
11 Ngidi
* I think that Hendricks is not yet a certainty. Markram is likely to threaten that one. Mulder at 6 and Preotius at 7 is also up in the air, Nortje ahead of Steyn is a huge call, but Steyn was largely ineffective in the ODI's he played in against Pakistan - few wickets and rather expensive as well.
As to the better WC squad I would play Markram as opener ahead of Hendricks and rather play Mulder at 7. Mulder and Markram can rather combine to be the 5th bowler.