The thing that tall PGs have to deal with is the dribble height. When you're tall, the ball has farther to travel for each dribble, and quality defensive PGs (Chris Paul), will make life miserable for Giannis. He's far too frail/thin/weak/slight to use his hips to keep defenders away from the dribble like Magic did so effectively. His handle also isn't nearly as good as they should be for an NBA level PG. In addition to Kidd trying to be smarter than everyone else, this reeks of a coach trying to put his best players on the floor, regardless of position and fit. Giannis is an incredibly raw player as it is, and should absolutely learn to be a SF, but he has Jabari Parker that should play SF, John Henson that should play PF (along with Irsan Ilyasova), and Larry Sanders at C.
It'll be interesting to see how Giannis does, but I have a hard time believing he'll succeed in the NBA as a full-time PG.