One of the things that I like the most about the DLCs is that they add new and interesting things to the game. The quests for the most part are good, showing a new perspective and story. Transplanting those into the main game is possible, and there are modders working on that *kudos*. One thing that I find would be really cool though is to include items/enemies from the DLCs into the TTW game.
[url=http://www.nexusmods.com/newvegas/mods/47880/?]this[/url] mod does a great job when it comes to weapons from new vegas dlcs. But I would like to see it taken a step further, as is it mostly addresses only new vegas.
Here is a list of items/enemies from DLCs that I think could make an appearance in either wasteland, and if so where. I'm not listing weapons, since I would like to see all weapons, perhaps excluding alien weapons from mothership zeta.
Chinese stealth armor (Operation Anchorage) in the chinese remnants around DC.
Raider armors (The Pitt) added to raiders, fiends, and other "raider" npcs across both wastelands
Factory protectrons (The Pitt) I particularly like their desing and think they would look better than normal protectrons in several factories.
Broken steel enemies added to the mojave wasteland
Workman coveralls (point lookout) as randomized wastelander armor
Fishing poles (point lookout) as random trash, where it might make sense
Moonshine (point lookout) it makes sense at least in the mojave
Nuka Colas Quantum, Victory and Quartz in both wastelands
Medical & Repair Eyebots (lonesome road) added to the enclave in the capital wasteland
MRE (lonesome road) in several military bases along both games
Giant Cazador (honest hearts) wherever cazador can be found once a certain level is reached
Green Gecko (honest hearts) in greener areas, such as Oasis, speaking of which...
Spore plants (New vegas) in Oasis
Nightkins (new vegas) in the capital wasteland ruins, some members of the master army could have ended joining the vault 87 super muties.
I don't know how easy or difficult this is, but I hope I picked your interest guys. Let me know if you need more ideas :D