The problem with Marchisio is he's a great player. But, in our system he obviously can't bench Pirlo. His two other 'rivals' so to speak are Vidal and Pogba. Both are currently better. So there is no room for him when we're at full strength
When Pirlo goes, a midfield of Vidal - Marchisio - Pogba could work, however not in a 3-5-2. There isn't enough creativity in that set up. In a formation with some top wingers however, it would probably work.