I don't think an ad hoc play-in tournament makes much sense in this context because it means that all other teams are effectively idle during that time, and the NBA needs to be able to squeeze as many essential games as possible into a compressed time frame. A play-in tournament is basically just creating nonessential games.
If they are going to do a tournament then just make it a 30 team knockout tournament. Give the Lakers and Bucks a first round bye and go from there