Sim, o final do Inception está aberto à interpretação do espectador. Confira esta entrevista de Chris Nolan. Sobre o final aberto Nolan diz que
I've always believed that if you make a film with ambiguity, it needs to be based on a true interpretation. If it's not, then it will contradict itself, or it will be somehow insubstantial and end up making the audience feel cheated. Ambiguity has to come from the inability of the character to know -- and the alignment of the audience with that character.
Quanto à interpretação do próprio Nolan, ele afirmou
I choose to believe that Cobb gets back to his kids, because I have young kids. People who have kids definitely read it differently than those who don't. Clearly the audience brings a lot to it. The most important emotional thing about the top spinning at the end is that Cobb is not looking at it. He doesn't care.