This year, the team has proven to be so flexible, and has been so successful, that I don't think the squad will change much at all over the summer.
Next year's squad:
Valdes (Pinto)
Alves Pique Puyol Adidal (Adriano, Masch)
Xavi Busquets Iniesta (Masch, Keita, Thiago)
Pedro Messi Villa (Iniesta, Afellay, new forward)
That's 18 players. Just like this year, Masch will probably get more minutes that at least one of the starters. Masch has a way of getting the other team so pissed off that they lose their composure, which makes him an extremely valuable guy to have on the field.
Thiago, Afellay and the new forward will compete for playing time. Though the squad is likely to include a couple more (Fontas and ?), these guys won't play much at all unless there are quite a few injuries.
The keys will be Masch learning how to play CB, Masch and Busquets learning to play together in midfield, and incorporating Thiago, Afellay and the new forward.
I bet the new forward will be either young or old. Not any superstar in his prime, someone who can handle usually not starting.