This is something that bugged me when I completed my first playthrough with the Yes Man ending: Yes Man says that you can shape New Vegas in your own image. I thought: "Great! I'll wipe out the Omertas and White Glove Society and bring in some new ownership!" However, that's not really possible. Especially in combination with a free play after MQ mod, I would love to see the option to bring new groups to New Vegas. For example:
1) You crush the NCR and oust them from NV. This leaves an opening at their embassy. Would love an option to see new groups in there to help with policing. BoS and the Khans could be options here. Boomers possibly as well. I know that BoS would cause friction with them wanting the tech, but would love to see an option for establishing an agreement with them that leads them to be able to re-establish themselves in the region with the PC's help, especially with Veronica as a party member (my fav companion). Would be a nice chance for them to get out of their bunker finally and into a position of strength.
2) Great Khans, Powder Gangers, or Fiends (evil PC) take over Gomorrah. Seems like it would be a good fit for them: drugs, prostitution, gambling, etc.
3) Kings overhaul one of the casinos--probably Tops with the theatre. Would love to see an Elvis-styled Casino (would require changes to the decor) with the King in charge and the Kings running things. They've done good work in Freeside and they could be rewarded by the PC for their efforts by being welcomed onto the strip.
4) Not sure about the UltraLuxe, but for a good PC would be interesting to have a "good" casino, maybe with the Crimson Caravan supplying the Gourmand and the FotA keeping things clean. Maybe the Nashs and the folks from Primm with their casino experience are asked to pitch in. Not sure if there are other high-class NPC options for taking this one over.
5) The Lucky 38 opens to the public for the first time in decades. The PC is in charge, but could have a manager run the day-to-day operations. Manager candidates could be important/interesting NPCs the PC meets along the way in their journey.
Anyway, this is just a thought, and I'm sure it would be a boatload of work to make something like this happen, but I think it would be sweet to actually shape NV in your own image and this would provide additional meaning to the PC's interactions with the factions surrounding NV. Rather than just tell Yes Man "these folks are ok" or "ignore them" it would be great to have a "I'm going to give this faction the Tops Casino" and "Let's get them moved in" option.
Even if this never happens, I would be interested in discussion on this topic.
Cheers