Locking yourself into the bad ending of a DLC for choosing the ending they didn't want you to choose in the main story? Now that's dumb enough to make sense.There is that, but I expect the punishment for choosing Devil will continue on into any potential DLC. Imagine some Bioshock style “I’m going to shoot you now” and they get to be like “Oh, are you? I don’t think you will, or even can.” BOOM, you’re Adam Smasher 2.0 now, kiss the ring.
That is, if they decide to do a post main story DLC at all, which I think is less likely the more I see