I like Wagner as a fringe NBA prospect who a team should take a shot at in the early to mid 2nd round range. Ultimately I hope he stays in school 1 more year and work on having a Frank Kamisky like senior season. Their stats as junior are very comparable. If Wagner continues to get stronger he could work his way into the first round next season.
As for the Celtics I do not think he will provide enough dynamic offense to make up for his defensive short comings and earn court time. He shares many of the defensive limitations as KO but is not nearly as over all skilled on offense.
I personally think the Cs will find themselves picking from a crop of talented but flawed guards/wings at the 27th pick. Such as Grayson Allen, Rawle Alkins, Trent Jr, Melton or Frazier.