Did someone say stats gobbling buffoon? It's funny you should mention 3 at the back because I was looking at it just yesterday.
As far as starting formations go, Pep has used 343 only 8 times in the last 2 seasons. However, more pertinent to your line of discussion about Zabaleta - he's played 3 at the back 26 times in 2 seasons. So it is definitely something we will see.
I completely disagree with your idea that he doesn't have the players to play 343 though, as he's got the perfect squad for it.
It's worth pointing out that he didn't use it in his first season as well - so either he adapted to the Bundesliga and his squad, and played 3 at the back because it suited them - or he waited 12 months until the players were all comfortable with his ideas, and they had the basics sorted before he started complicating things.
IMO we will play 4141 mostly aka 433 with a single pivot. It's by far Pep's most used formation over his career and this season. Gundogan as pivot, 2 attacking midfielders in front of him, full backs tucking in to support the pivot and out and out wingers staying wide.