Aside from the spectacular goal last week, one great individual effort earlier this season that led to a goal, and some very impressive attacking that gets himself into positions to offer up some assist opportunities for the strikers. I'd be interested to see what more to his "end product" he would deliver if he was given some more PT.
Again, do you think Marchisio believed he couldn't contribute to the team equally as a 19 year old? Marchisio was on fire Conte's first season then had an unfortunate span of injuries that Lion brought up. How else is a young player expected to get better? By getting experience. Now, Juve must seem to think the kid is good enough for the first team because he is still here and hasn't been loaned out to get experience so there is obviously a spark there somewhere.