Something like this. We can find space this way behind Pjanic and Alex Sandro. Suso needs to be vigilant in midfield making sure Khedira doesn't run the show, but can also peel off whenever get the ball as there will be a ton of space behind Alex Sandro. Same with Hakan and Pjanic, especially with Rodriguez overlapping and pulling Cuadrado away.
If Allegri is feeling weak, i'd expect him to drop Dybala and play another midfielder in a 433 and bringing on Dybala late if they need him. This is way too much space for players like Suso and Hakan with Kalinic being incredible at dropping back and spreading play wide. Especially at home with the crowd, I really don't expect Allegri to risk playing his 4231 here.
The difference with what Montella is doing and what is typically being done is this:
Usually when your FB/WB takes the risk to bomb forward, the team shifts to cover him but they do so with a man down, so if its a 4 man defense, they shift to be a 3 that's spread thin, or are forced to have a midfielder cover back. This also means that attacking WB needs to make sure that he rushes back once the move is over to maintain the original shape. So you stretch with the move, and are forced to revert back once its over as fast as possible to not leave any space open.
With Montella, since the formations are so fluid, we can maintain our shape not by players going back to their original position but by shifting formations to cover the space. Rodriguez decides to attack suddenly on the left and ends up really high up, but we lose the ball. He doesn't have to sprint back wasting energy and focus, as he's now the LW in a 433 and Romagnoli is already covering for him as the new LB with Musacchio, Zapata and Borini the new back four. Rodriguez stays up as the LW, tracking Lichtsteiner while Suso tracks Alex Sandro on the other side in a standard 433. Hakan, Kessie and Biglia in the middle. If Borini decides to attack the right wing and the same thing happens, well now the back four is RR, Romagnoli, Musa and Zapata. Hakan LW and Borini RW, with Suso helping out in midfield.