Thanks for posting and do not let what I am about to say discourage you from future posts.
For now the circuits are the same phase, but for future trouble shooting or renovation work, no one can insure these two circuits will remain on the same phase.
We can "what if" any electrical installation to a point it will be dangerous.
Take multiwire branch circuits, there is nothing to prevent some one from moving these onto the same phase which could overload the neutral.
That aside I like your suggestion and it is done around here for multi family dwellings with no landlord panels, I have seen it done with 3 lamp fixtures with one lamp powered from each of the 3 floors of a 3 floor walk up.