I do remember an interview years ago where he mentioned that folks in Legion territory where pretty safe.
I think it's an interesting idea and one that I would have liked to have seen explored.
If a New Vegas sequel ever did happen (and not taking the TV show into account), I think it would be interesting to explore the fallout of the death of Caesar and how those territories react to a crumbling legion. Maybe there is some kind of spite for the Courier while others look up to them like a folk hero.
I can imagine dedicated aspects of those areas forming their own copies of the legion, but not having the charisma or power to really pull it off.
Actually, I should write that in a fanfic at some point...