I doubt many people would have picked Vincent Kompany for today's game. Pep did, & look at the outcome ( which is another example of how it's impossible to guage how he sees things).
I think he wants to play 3 at the back sometimes, but I think most of all he has wanted 4 decent centre backs in the squad, to do with, as he sees fit.
Over the course of this season, Otamendi has become the No1 cb, but before his injury, Stones was looking like becoming that player (unfortunately he has been reincarnated as William Prunier, since he came back but hopefully that will soon blow over) and today, imo, we saw the best performance of the season by any City cb, by Kompany.
Pep has two fairly young cbs, who 'could' grow to be a fantastic pairing, but for all we know, that could be 4 years from now & he decides Kompany & Otamendi play all the biggest games from now on, until VK gets injured again.
The point being; I don't think Pep cares. It will be down to how well the players play & how suited they are to the opposition.
Otamendi will be first choice if he merits it. But if Stones, Laporte, even Kompany, merit it, they will get the nod. Pep, imo, will try to have 4 'partners' who can all play as pairs, & if one doesn't perform consistently, over a season he'll demote him then sell him. Even Stones or Laporte.
We now have 4 players, fighting for the shirt. Which is brilliant.