I really hope they don't add a post-ending DLC. Games like these become boring when there's no difinitive ending, no major peak in the game history.
pre-ending DLC's would be very welcome though. Something with the enclave perhaps, or visiting old F1/2 areas, area 51, a gangster DLC etc. etc. There are so many options.
That being said, if Obsedian makes a post-ending DLC (which i really hope they dont), i sinceerly hope it's gonna be alot better writing than Broken Steel was. God that was one awfully written DLC.