We are going to crash with this formation eventually. Too many issues with it.
Firstly, too much space around the back 3. Every single 1 of our back 3 (even Chiellini) was skinned at least once over the past 2 games. This will continue to happen because a back 3 is not nearly as compact or in unison as a back 4. Not to mention none of them are quick players, and speed is an asset when more space is available.
Secondly, our weakest area of the squad since serie b has been at fullback, and now we have a set up that places special importance on this area of the team for the formation to function. Makes absolutely no sense at all, and with the way our wingbacks have been playing so far, they might as well be fullbacks anways. At least that way we have an extra player in midfield (where we have some quality), and get to avoid all the problems of the 3 man D.
With 2 competitions, I don’t see how this is going to work. We only have 3 natural cb's, and they will all play when fit. At least with 4 at back, 1 is always rested and ready to step in should some1 get injured. I don't see Zebina as a good choice back there. He did alright vs Genoa, but there were many instances when he was easily beat and Momo/Caceres had to bail him out. Canna is not even an option on the right side of 3 man D imo. He needs to be in a position where his experience pays off, and that is at cb in a 4 man D.
I think (hope) Zac is holding off until more midfielders return. When Camo, Marchisio, Melo, Momo and Poulsen are all fit and back from suspension, you want 3 of these players in midfield. No coach in their right mind would sacrifice any of the above midfielders just so he could field very average wingbacks.