I think Novac would be an interesting place to set up shop. From my own play, I found that there's anywhere between 1 to 4 traveling merchants there at any time. It'd be nice to see some barter going on as well. For example; when you set up shop, you can set an NPC to operate it for you, but with guidelines of what you want. You'll of course get caps for selling your wares, but you could also tell the NPC that you're interested in trading for ammo, guns or even junk items. As time goes by, the NPC will slowly build their supply of that item, trading with the traveling merchants.
Eventually, maybe one can even buy their own caravan and have a couple of traders head off for extra funds. You could even supply the guards with stronger armor and weapons.
Yes, Novac could work... You could use the gas station there as your shop! It's not used by anything, as far as I know. I don't even think any other mods out there make use of that place...
Go there, clean up, invest come caps, hire an NPC and so forth.
Could end up being an entertaining quest, should someone take it up.