"Can" and "should" are two different things. While many of the Wing responsibilities are interchangeable in the Carolina system, not all are. Some guys can go back and forth well, some cannot.
Here's the best comparison I can give you:
Did you see Wayne Ellington or Donald Williams play even a minute of 3 at UNC? I'll answer that for you --- no. There was a good reason for that.
He "should" if our personnel dictates that he should. No more, no less. If Johnson leaves, we sign Langford, and we don't add another wing, he'd be the closest thing to a 3 on the team.