Allegri is convinced by 4-3-1-2 and is not expected to revert back to 3-5-2. 4-3-1-2 vs Olympiacos was not created last minute but it was practiced in training many times - GDS
Better late than never. It took him too long IMO but here it is at last. With this formation we played very well despite the nervous game vs Olympiakos a coupe of days ago. It was a pure joy to watch our players pass the ball around with more accuracy, faster and also more imagination. It's not all perfect yet as we were very wasteful upfront and the movement wasn't good enough just yet but it was already very promising in comparison to the obsolete 352 which in CL was always a 532.
But now we need a trequartista. Tbh I'd prefer to see Pogba there instead of Vidal but in longer term we need a different kind of player - faster, more explosive and better at 1v1. Besides the 4312 is all about the midfield that's why it'd be unwise to play all 4 mids all the time (Pirlo, Marchisio, Pogba and Vidal). Pereyra, Coman and Govinco should be tried out in the treq position because I think we'll have to go on with what we have right now until the end of the season. Players like Mata or Shaqiri aren't attainable in January and Berardi should stay at Sassuolo until the end of the season.
I've seen glimpses of improvement from Pirlo. I'm glad grandpa Pirlo can still be useful and he can partly thanks to the 4312 IMO. It takes a lot of pressure from him as we have more advanced players and he can do things he does best: move around defense and spread the ball with a lot of accuracy thanks to the fact he's got time to do it his own way.
As for wingbacks I'm glad they're moved to the backline. They definitely had too many duties and they're not good enough at attacking. They can do their thing in defense though and thanks to that the 3rd CB became unnecessary.