Its possible we will sign one of the young keepers next summer if Buffon really retires, like Meret or Scuffet. But cause both are italian and "promising" there will always be that "is this the next Buffon, the next numero uno" so we also prepare that a 21 year old (Meret is 20, Scuffet is 21) might not be totally ready for a big club like Juve instantly so first season is settling in while Szczesny is starting potentially.
Some people here are just random haters who hate players who are not at Juve. Szczesny had a very good last season for Roma.
Im not sure if Donnarumma is really realistic long term. There have been some stories like he dislikes Juve and he made some negative comments about us. With their takeover and improvement, he might stay there or go to a Real/Man u in couple of years time.