Now on topic so I'm not a bit of a hypocrite. Of the ideas you have posted that I can actually read the only one I somewhat like is vehicles and that is a big maybe and more nostalgia for Fallout 2 than anything.
Time travel is a no so that eliminates your first two ideas.
I don't know what a cyco is so I don't particularly want them to have their own land.
The ending should stay definite, in order to pull off open-ended gameplay well it would take hundreds of man hours to implement all of the changes caused during the course of the game and without those the end is totally meaningless.
Underground monsters? We have a little bit of underground and there are already monsters in it. Problem solved.
Maybe some slaves could enslave their slavers but I really don't see why.
I think most of the towns near New Vegas are in or near extreme famine so that one is done too.
Why do you want something to do with cows? There are already Brahmin, aren't they enough?
We already have a forest coming out of nowhere, one of the vaults.
They are probably going to extend the map already to the west a bit.
We should only go to Area 51 if it reveals the government has had no contact what-so-ever with aliens and totally retcons Mothership Zeta.
Operation Anchorage, once again, why?
And the one I have been waiting for: Enclave. NO. They should stay dead and gone. They should have stayed dead and gone after they were definitively wiped out in Fallout 2. Considering what happened in 3 they have been double wiped out and really should not come back. Come up with new villains people! The Enclave were fun the first time around but after that they got stale. A remnant or two was nice and more than enough.
EDIT: I want to add that I agree with TestECull's statements.
