I doubt there will holsters or anything of that sort in New Vegas with the limitations of the Gamebryo engine and all that jazz, I'd say that is something we may see in Fallout games to come but not in this one unfortunately. :tops:
As Madcat said, they did it in Oblivion, can't be too hard to do with the current engine, but then again I've never worked with the engine and have minimal knowledge of modding and what not. Well, it definatelly won't be in New Vegas, hopefully Fallout 4.
Wouldn't it just require a redone holstering animation and then just the holster mesh with reworked skins for different types of guns? For rifles all we need is a sling that fits over each outfit like in RDR.