The 2019 series losses against SriLanka must have forced the situation about team selection. I think Smith and Boucher may have taken a stand to the effect that the performance of Elgar and Du Plessis - two obvious failures in 2019 and under-performing since then - is making their positions untenable,
A further problem is the offer to De Kock to captain the team met a frosty reception. De Kock initially did not want the captaincy - he is already unhappy that he is given poorly selected teams to captain. So there must have been some serious talks about especially team selection to accept the captaincy despite his initial reluctance - so he might also made demands as to what the team should look like for him to accept the capataincy,
It may well be the case that we will see an entirely different team taking the field tomorrow and even that Du Plessis and Elgar be sitting in the stands tomorrow.
As far as the Proteas are concerned the team is even in a worse condition was in rugby when Erasmus to take it over, and I think that the time to rebuild the squad is starting immediately, Rebuilding cannot be done with too many over 30 players in the squad
So watch out for the following new players being in the team tomorrow:-
Van Tonder, Verreinne, Mulder and M Pretorius