Offensively it's not wise to feature KG at the 5 unless it's in crunch time. You don't want to take him away from those sweet spots at this stage of his career. For instance, we watched him wear down in the Miami series while trying to consistently establish post position. That works to the detriment of his stamina, which hurts his outside shooting touch. Nevertheless JJ should be given time with the starters and using him as a non traditional, athletic center could be an experiment Doc may be thinking about. He does have a post up game, and would catch on a lot faster playing alongside KG ... and we know what his defensive quarterbacking did for Perk.
JJ starting could also put less of a strain on Jermaine. Now if Davis is resigned and perhaps they make a run a T. Young or Batum, they compromise size, but gain more length and athleticism along with Green on the front line. JJ may not be finishing games or be able to defend legit centers like Howard, but spotting him starting minutes the 5 makes sense.