I personally don't see him as a signing we should make, if he's available as an opportunity, sure, let Beppe have his fun, but I don't think we should spend too much resources on him, I'm very pessimistic about his chances at Juve.
Allegri benches pretty much every youngster that comes his way for almost half a season, my bet is that Keita's ego couldn't survive even one month of that. Even if he miraculously kept it together, I don't think he's good enough to eventually bench Dybala or hardworking enough to play as the winger in 4231. If we change formation, there's still a lot of competition for him to overcome. A guy with his arrogance and attitude is like the worst possible bench option