Theory #9: Cobb dreamt of the final sequence while still in limbo with old Saito.

This theory is plausible only if one assumes that Cobb was in limbo with old Saito for a significant amount of time. The idea is that when they were waiting for the sedative to wear off, Cobb went to sleep and dreamt of the final sequence that we saw in the film. It was an unplanned dream (he was not connected to a dream machine) but it was not what I would describe as a “permanent state of being” because he would eventually wake up either in limbo or in reality, implied by the cut to black at the end.