He got a some CB time late last season (kicked that Dangerfield like goal running our of the middle).Going back to Darcy's draft footage, he didn't do well as an inside mid. He'd very often dispose to the nearest person rather than teammate which damaged his overall DE numbers. Given what he's very good at l don't see any justification to put him in the packs and should remain a receiver and runner.
I think Darcy will eventually develop into that burst from stoppage player that we all crave. Very similar vibes to Holmes.
Don't forget that most of his underage footy he was a skinny little runner... he has put significant size on even since this time last year.