Yeah I'm sure this wont be an option.

It would take too much effort that Bethesda isn't willing to invest. Settlement building seems to work by building actual houses and farms and buildings. This could be converted to something that makes more sense in a vault (renovating sections of the vault and using them as homes, creating an indoor greenhouse etc) but that's something Bethesda would expect modders to do.

The main problem is that settlements seem to all be in the open world, while vaults are, as interiors, behind a loading screen. It would be a little iffy getting raider attacks to work if they have to load in to a new space which likely has multiple levels and loading screens within it. Again, it's totally doable, but not something I can see Bethesda caring about.

Well considering in the gameplay Videos they had a brief screen of what looked to be a settled vault I am willing to bet it may be possible. I am just glad to see that vaults initially look to have more different floor design types this go around.

This. Fallout Shelter is an excellent overseer tutorial on how to run/simulate and/or recreate historic vaults from Fallout lore IMO. Imagine trying to recreate settlements around some of the whackier vaults like vault 69 or 22. Then playing the role of a xenophobic Vault 101 Overseer who shuts the Vault off from the outside settlement and world. Thereby leaving the settlement NPCs to fend for themselves from raiders etc.

Or perhaps you're an enlightened Overseer who is open minded enough to encourage vault dwellers to trade & interact with the outside world. And if you're really good at playing FO Shelter, you might transition these management skills to building a successfully interactive FO4 settlement the likes of a Vault City

Either way, just the process of trying to balance life/happiness/survival of the vault dwellers while defending/ignoring the settlement & outside world would be a challenge mini game in itself.

Jury's still out on how much of an economy the settlements will have yet. But being able to setup trade routes using brahmin trade caravans between settlements you build is definitely promising. I hope the trader NPCs will bring back hard to find/non local items and goods not native to the region in their caravans. It would be cool for example to live in a landlocked settlement in the map's interior. But the NPC settlement would have access to sea food and building materials not local in the area through the trade caravans. That would definitely make for a dynamic game economy.

The downside to this is that using Vault 111 may not be a good idea (even with mods) as is being suggested by some folks.

It's probably going to be a lot safer and better modding practice to reconstruct a vault from scratch (one that is more 101 vs. 111 style) using the vanilla textures provided from 111 and other vaults. And in the areas which we'll be restricted to building like Todd said. I'm really pumped on rebuilding a settlement as close to Vault City as possible. But I suspect the scope of this will be limited to what Beth restricts the buildable areas to

Anyhow, I'm just hoping they allow us to build near a large body of water like a lake or even the ocean. That would provide a limitless power supply source (if we can use water as a source to directly generate electricity like they showed us in the video). Because I'd love to have a secret underwater entrance that allows me to directly access my home inside the vault. Similar to the amazing UWHNV customized home here:

http://www.nexusmods.com/newvegas/mods/36121/?

where you could acquire the re-breather and wet suit from the Boomer quest in New Vegas.

Or perhaps and underwater entrance that leads to an underground docking area which doubles as a secret, illegal arms/drugs market. And NPCs could sandbox selling their shady goods there which they can't do in the legit markets I'd be building on the surface

True. That said, in-universe, I think a Vault's infrastructure would be much preferred when it comes to picking a place to settle down rather than starting up a settlement from the ground up.

Fair points, but I'd still be wary about living there myself. If your defenses do get compromised, you're completely screwed. The enemy could turn the lift into a killing floor, or just break it and trap you. I wouldn't want to live anywhere that didn't have more than one way in or out if I was expecting attacks.

On the other hand it is a vault, so you could just close the door and wait for your enemies to die of old age.

That would be a great plot.
*opens up vault door, sees raiders shooting each other in the face*
"Screw this, I'm going back to sleep."
*reenters vault and goes back into the cryochamber. Fallout 4 ends*

At which point I as the besieger find a way to collapse the cave or fill the lift in or whatever it would take to permanently seal the Vault entrance. Sure, I didn't get any of the goodies, but those goodies are finite, and eventually the Vault is going to become a mausoleum.

No reason you couldn't dig yourself out. Even if it takes generations.

If a Nuclear bomb didn't do it, whatever the besieger comes up with wouldn't do it. Really If someone has the resources to breach or seal a vault from the outside. NO wasteland settlement you built from scrap is going to stand a chance.

Courier Six was able to destroy Vault 19 with five blocks of C-4 in a sulfur cave. I don't think the fact that mountains that were non-targets for the nukes weren't destroyed by the nukes means that people with explosives wouldn't be able to cause cave-ins and collapses.

from all i see how they're constructed, a simple plasma cutter should actually do.

don't see how'd you pose much of a threat to any settlement with one though.

The caves were filled with potassium, and the explosives are placed deep inside in a strategic location. Heat+potassium+water equal huge explosion. And given the Vault was built into the sulfer caves this is a case of destroying it form the inside not out. The Courier can just as easily kill everyone in the Vault because the caves provide a back door entrance. Cave in's and collapses can of course be cleared and one could assume a vault has equipment for clearing rubble if its entrance is buried.

And again what settlement could you build in the post war era that would be more secure then a vault? If they can breach the defenses you put around the Vault door then they can breach the defenses you put on your settlement in field X.