well there is a locked gate at the mojave outpost in the southwest that can't be opened, but if you go west then you are just in california and the other fallouts already covered that, so going east to texas would be a good idea if you ask me
If you want to get technical, east of the in-game terrain would be Utah and southeast would be Arizona and such, Texas, by Fallout canon standards would be a very long walk.
OT- Id like to see something that adds more overall area to the map, it doesnt have to be alot, just give more places to explore, more people to meet, more quests. Basically, standard DLC things. I also voted however for something like the system that was used for Op Anchorage. Maybe be able to get into a VR sim and get to do something on that level again would be nice. Theres my 2Cents