Main formation is 3-5-2
Season starting formation is 3-5-2
When all cm's are fit and back, we might move to 4-3-1-2 depending on Pjanic performances
If Dybala is rested, we'll certainly either go 3-5-2 or very offensive with 4-5-1. Both using a trequartista and having ALOT of offensive movement off pogba
What we wont do is go 4-3-3.
4-3-1-2 is very likely, but will depend on Allegri's assessment of Pjanic and his performances as you said. Personally, I don't expect any formation without the 3 man midfield to be used however, such as a 4-5-1. The closest we came to doing that last season was the first Bayern game with that "4-4-2", which was more of a 4-3-3 / 4-3-1-2 hybrid, with the only winger being Cuadrado on the right. It's possible that with Marchisio out a shift to a 2-man midfield could happen on occasion, but in my mind it makes more sense to use a 4-3-3 if a player comfortable on the left wing is purchased, or a 4-3-1-2 if not.
P.S. Ageed on 3-5-2 being the main formation.