Barzagli never played that did he? We tried Ogbonna and Marrone only there in the past. Rugani I figured could be tried, but he seems bit conservative with possession so a ball playing role like Bonucci's is perhaps not ideal for him. Which yeah makes resting Bonucci kinda impossible in our current set up.
I remember Barzagli playing there once under Conte. But yeah, that's once or twice in 4.5 seasons. I don't think he'll have any trouble playing there though. He plays the same cover role as Bonucci when paired with Chiellini (the gung-ho stopper) in a back-4. With the ball, he might not be as good as Bonucci and might not have the range, but he isn't bad.
With Rugani, Allegri doesn't seem to trust him anywhere besides RCB yet, lol. Wouldn't play him on the left either. And so far, has only played him vs weaker opposition. Caceres started against stronger teams.