In the course of the Leviathan DLC you learn some pretty important new facts about the reapers, namely that
they, or at least the Catalyst, were created by the Leviathan species, and subsequently rebelled and nearly destroyed their creators.
Does this knowledge affect the game ending at all? Are there more conversation options with the Catalyst, or does he/it offer up any additional information?
I would test this myself as I've just completed the DLC, but there are several hours of gameplay between this point and the end of the game.