He can shoot, but he will not be a big time scorer in the NBA. I do feel he will be a reliable 3 point threat from here on in. He still needs a game in the paint, like a floater off the dribble, a fall away in the paint, and just flat out getting to the rim. etc.
Marcus Smart should be able to average 15 points a game, 5 rebounds, 6 assists, and 2 steels for years to come. That, along with his already smothering defense, a defense that is still developing mind you, will be a lot of fun to watch.