How about a mini DLC where you can rebuild a motor bike (and maybe the side compartment for companions), powered by fusion batteries (probably). that would essentially be the DLC, but for free and it's mini and combats my least favourite aspect of the game on playthrough number 3 (the endless wandering).
As a more full DLC, similar to Broken Steel, continuing the wastelands economical development and security based on choices you've made, strengthening trade caravans, and helping set up trade routes around the wasteland leading to special weapons and armor and discounts. Also taking out remnants od the majour players you didn't side with.
I'm out, however, I remember a few places that I wouldn't minde being expanded on, just not off the top of my head (crashed top side bomber aside).