This is my opinion:
Unfortunatly the football is money, courtois is an excellent GK, and the chelsea won't leave him.
Juventus: Buffon will leave after this season, but I think Donnarumma will join juventus. If Donnarummo won't go, they have szczesny, last year he played a solid Serie A with Roma
Real Madrid: I think Real will wait for De Gea, He has not already sign a new contract, and Real will try to keep him from Manchester (he is spanish too, a real Casillas's successor)
PSG: Eh... the money. I can't predict nothing with this team, if they will want courtois, I think they will take him, but Trapp is a very interesting GK. Also they have Areola, I think courtois will fill too much the GK's position