Well, I disagree:
- Baynes is currently in great playing shape. He doesn't need to go Austin to get in shape.
- Baynes will mostly set screen and play some pick and roll on the offensive end. To do that, he doesn't really need to learn the offense and going to Austin won't really help him in that area. Even if Toros theoretically are running Spurs offense, it's far from being the case in reality and the drop of quality between NBA bigmen and D-League bigmen is just huge.
IMO, Baynes will sit at the end of Spurs bench as soon as he is signed. He will mostly play garbage time minutes at first but he could see his role being expanded if he is doing well. He could be send down to Austin but more for 1 game stints like De Colo than for an extended period of time like for Joseph.