After watching every game of Marcus' career, a few things to point out about his D league play. His transition decision making and inbounds passing being strengths are nothing new. Arizona is a big time fast break team so he's had plenty of practice adn he was lmost always the inbounder on out of bounds plays since he really isn't a catch and shoot guy.
I would be shocked if he ever develops the NBA 3, and I think it behooves the Toros coaching staff to get him to stop trying for now at least. He had problems with the college 3, and every possesion where he attempts an NBA level 3 is a possesion where the only positive that can possibly come is Ian working on offensive rebounding. Also, if he is able to not shoot that 3 then he is working on his mid range game and creating for others, which would truly be his ticket is he is ever to be called up by anyone.
Also, in a half court style game, expect Marcus to lead the team in turnovers. He doesn't really understand how to use his strengths in a half court game, and the process of figuring it out will no doubt be messy.