Murphy spends more time explaining why it won't happen than arguing why it should. I mean, it's all fun to consider, and it was more fun back when nobody cared about service time or even being so careful about development and you got Marty Bystrom.
But still, at some point there are only so many pitching spots to go around. They are about to get Seranthony, Eflin and Wheeler back, so that means Sanchez (remember him?), Nittoli and quite possibly Coonrod (or Nelson) are already gone. And you probably keep Falter, so is that a six-man rotation or does he replace or pair with Thor? And if the former, is Thor a reliever or does he pair with Suarez? And then you've got McGarry who is already older and more experienced and not on the same innings limit.
To just bring Painter up as a reliever or tandem starter for all of two-three games doesn't even seem like it would be that valuable, or necessary. Is it going to help them go 4-2 against the Braves instead of 3-3? Make the playoffs by four games instead of three? Keep them from missing the playoffs? There are too many other players and pieces involved for any of those answers to really be yes.
Now, if he was available and you just wanted to put him in the rotation and let it rip, that would also be fun.