If we want to compete with Bayern next year, we must strengthen our MF with a physical player no matter what he costs,remember what Bayern did with Martinez, they needed that player, they got him and won everything.
Vidal is just the PERFECT one for this as he is very skillful too, for the playing time we can just rest Xavi like he never did as he will be 35 next year, don't forget that we have a little number of injuries this season and that a long term injury is never excluded.
If the board really wants him, the big problem is that Pogba is very likely to leave to PSG or to Madrid, and Juve will never let 2 key players leave at the same time.