It's going to be a real revolution of sorts next summer, and you can almost see already who we would be looking to replace players with. The 18-19 summer mercato has been very well planned in advance of important stalwarts leaving (Buffon, Barzagli, Lichtsteiner, maybe Khedira) and leaves us with room for a big signing or two, if you consider that we have Szczesny, Caldara, Spinazzola and Lirola already on our books, players who will surely step into vacated roles in the team. Making moves for players like Can, De Vrij and maybe Keita on free transfers is shrewd and gives us strong options.
I imagine Liverpool will finally do a deal for Naby Keita next year for some ludicrou fee so Can, whether he is attracted to Juve already or not, probably sees this in advance.
BTW other players who have expiring contracts in summer 2018:
Messi (lol)
Alexis
Isco
Jose Gimenez
Goretzka
Iniesta
Laxalt
Bold linked before, worth keeping an eye on. Also a few others but cold rumours.