Expect the New Vegas strip with playable casino games, about a quarter of the map, a few spots to build your own home, and creatures and weapons and things.
You can download the initial 'early access' version from Nexus Mods. Nice casino, shame if I had to murder everyone in here. They say they 'aim to faithfully recreate and remake the Mojave Wasteland true to the original and open to the public to play with, explore, mod and build.' So when it's done, it could be the foundation for interesting newness. The modders explain that they 'intend to open and recreate some of Fallout New Vegas's map as a new explorable location as a addition to Fallout 4', a hub world sandbox sorta thing. But to manage your expectations: it is not an attempt to recreate Obsidian Entertainment's game Fallout: New Vegas inside Fallout 4. A new mod named Project Mojave is attempting to recreate a lot of the post-apocalyptic Sin City and surrounding areas as a Fallout 4 mod, and you can play the first slice now.
What happens in New Vegas stays in New Vegas, they say, though New Vegas itself will not stay in Fallout: New Vegas.
