Agree. Fast track him . Leaving aside Guelfi, of the younger players we tried this year, in the glimpse I saw of him, Mason impressed me as the one who now has the aggression, power, speed, skills and body shape to make it as an inside mid at AFL level.
Forget training him exclusively as a defender, give him a preseason with the mids and see how he goes. He should be a capable medium defender who we can run through the midfield rotation. Because all our mids need to be good defensively and run both ways.