I think the target is to end up playing this team at home against weaker opposition.
I'm pretty sure Pep usually likes to play 3 at the back against a 4231. That's why he's gone all out for Stones and Bonucci, because it's essential to have centre backs who are comfortable on the ball to play that way.
Also this shape is the best way to get Silva and KDB in to the same team operating in their favoured area of the pitch.
Perhaps KDB will play further forward as he is a bigger goal threat, but Silva would take the piss in that team. Having two energetic grafters behind him who have the quality to get the ball in to his feet, KDB nearby on the same wavelength, real penetrating runs with pace out wide from Sane and Sterling for him to feed, and the movement of Aguero pushed right on the last man, we could actually score 10!