Open World Mod. Possible?

I remember him tweeting that it's just a large lot. I think he's really good at promotion and drawing hype, but it's a lot built with all of those venues. You could do that yourself with what we have. What I am interested in though, is it does seem as if he's put it in a new world and I'm interested in that. I'm also curious as to the lot type he's used so all of the different areas function as they should without hiring NPC's.