Juventus made a big mistake not signing Verrati. From all I have read, he is highly rated and has a lot of potential. 12-13M was not that much. Juventus paid 9M for Elia to have him warming the bench.
The way I see it, Verrati at PSG can go two ways. Most probably he wont get enough playing time to develop as player. PSG wants results now and their model is similar to City, no space for youngsters. However with ancelloti as coach, things might be different. If he fails at PSG, he would disappear at middle team tables and never again interest Juventus. If he succeeds, his price is going to go up 3x-4x. Similar to what happened with fabregas.