maybe it could create a positive rivalry between the two of them, which can reflect on them scoring many goals and helping the team, I remember when I was watching real madrid when both Benzima and Higuain were playing at real madrid and they showed some really good football, two players competing with each other in the same team can go very bad or really good, there is no in-between.
I agree that it is certainly something that makes sense for Juventus. Don't get me wrong I am not supporting Cavani to be a great player, but Juventus just lost a great player and they could use another decent player, plus he doesn't seem to be an expensive one neither because of his age, so I would assume that he could very well be a great player for what they pay for him, can get him nearly for free now that United as Ronaldo.
Of course, this will have to wait until winter break and it also depends on what Cavaino does until that date comes, if he plays too well then they would have to spend too much and they won't do it, if he plays not at all or plays and plays badly then they may not want him. The only possible way for this to happen is if Cavani is a great sub that comes in and has few goals under his belt, that would make them spend 5 million to 10 million to get him.