I'll spare you the film student in me and give you the quick and dirty:
I think it's written so that the audience has to use their imagination and confront their own ideas to form the story. By not writing in a back story (how has this technology been created? Who pays them? How do they learn this? etc.) Christopher Nolan is asking (actually, requiring) us to think on a different level, or on more than one level (like the levels of the dreams or subconsciousness in the film). He requires us to project ourselves, or at least our imaginations into the film. In a sense, we too are the architects of the film.
To that, the ending isn't written. The only actual ending exists in the mind of the person you ask. There is no right ending because, like Dom's journey, the ending is intensely personal.
I don't personally think that it is option A or B. I think that the movie was largely a heist movie, however, I think that maybe there was more than one heist taking place. I think that the inception job on Fischer was also turned into a job to make Dom confront his deepest sub-conscious (once the second level kicked in and Dom was made to play Mr. Charles). I don't believe that the audience is supposed to feel as though the whole story was an exercise in futility. Typically a good story isn't meant to make the audience feel like they were tricked into watching and contributing if it's going to end up all for nothing. To that, I don't think the whole story was just about the journey of Dom.
The fact that there is no final "kick" for Dom lends an interesting possibility that somewhere he is still sleeping. The question now ends up being; does he know and accept that he is still dreaming?
