I hope this will never happen, Allegri was the "mentor" of Pogba he was a friend of him and if he will go there Paul maybe will think on his position and his contract with Red Devils.
I want Pogba back at Juventus and Allegri to Manchester can be an obstacle for the coming back.
Allegri would be a good appointment for United, it’s a poisoned chalice there though since Ferguson left. I’m not sure who will be tempted to take the job.
We have great examples of Italian coaches signing for English clubs. In the past Carlo Ancelotti and in the newest years Antonio Conte. They all brought amazing results for their clubs. I hope Allegri would be in charge of the Red Devils as I am more than sure that he is going to make the club competitive again.
Do not hope too much from a new manager to make a big change in the club. Here we are talking about United which is a Top club but their performance is still unstable since Fergie decided to stop managing it. Allegri could be the best option at the moment but I doubt he will be able to make United become competitive again in short time unless he makes a big change on the squad IMO. For me, with the recent United's squad, it will be very hard for any managers to make them become competitive again.