The problem is that if we join their ranks then we don't really have any choice.
If NCR says "Go to Camp Forlon Hope" and you disobey them then you might get court marshaled and hanged.
Being an outside contractor we have the choice to go and do where/as we please.
A way around that might be, if we were brought in as, say, a 'rookie' under one of the NCR Rangers (or better yet, a Veteran Ranger), then we could still kinda go where we please, since they're meant to be on their own for the most part, and it might take a Ranger awhile to get to a new area because of enemies, or another situation might come up.
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My personal ideas for DLC would be:
In a DLC involving a faction with high technology (BoS, Enclave, ect), during the normal course of the quest, we would have to repair a Vertabird, and get someone to fly it. After we beat the DLC, we would be given a radio (similar in the way of the NCR Emergency Radio) called ''Vertabird Radio''. When we use it, the Vertabird we repaired would come down in a nearby flat area (essentially the same way the NCR Emergency footlockers 'spawn' nearby when we use the radio, the Vertabird should land nearby, away from enemies, in a relatively flat area [if the area was just too rocky or had too many enemies, you might get a message asking you to clear out the enemies/ move to a new location and try again]. When the Vertabird lands, you can go inside of it, just like the one in
Broken Steel, and we would be able to walk about inside of it (yeah, I know, its small, but still). Inside the Vertabird, it would be outfitted for Recon missions instead of troop transport - instead of like the interior we say in
Broken Steel, there would only be 2 chairs, not including the pilots and co-pilots chairs in the front. In the space now opened, there would be a Armor Locker, a Weapons Footlocker, a miniaturized (or maybe high-tech, and therefore small) Work Bench and Reloading Bench, and maybe a small footlocker stashed under a seat for misc. items. Initially, there would be nothing in the lockers (although there might be a reward from completing the DLC inside of the lockers, maybe a unique set of armor or a good weapon, but that would be it).
You would then be able to fill up the weapon and armor lockers with your own gear, allowing you to have on hand much more than you normally could when just exploring. Run into a radioactive hole in the ground? Call in the Vertabird and equip yourself with a radiation suit. Run into some deathclaws over the next hill? Call it in and grab your Fat Man or other heavy weapon of choice. This would be a very nice addition, and also allow you to change gear in a few minutes instead of traveling all the way to the lucky 38 to get gear you stored (although I realize some people store gear in other places, but still, you'd save time).