Here is what I have to say on it... For the longest time I've been against any FO setting that was outside of North America; I still feel that it should only be that way ~however... In the case of optional DLC I do see an option.
The option would be a Vault constructed for military brass and their families, and have it someplace off the coast near Italy ~ like http://maps.google.com/maps?f=q&source=s_q&hl=en&geocode=&q=Pianosa+italy&sll=30.032996,-89.882563&sspn=0.503501,0.917358&vpsrc=http://forums.bethsoft.com/topic/1445842-dlc-outside-of-the-usa/0&ie=UTF8&hq=&hnear=Pianosa&t=m&z=13 for instance. /rolleyes.gif' class='bbc_emoticon' alt=':rolleyes:' />
I feel that this might be able to work as it could plausibly depict a pocket US (inside an almost Spaghetti Western) setting; replete with the 50's-esque attitude and iconic imagery ~like B52 bomber husks*, and power armor with pre-war pin-ups on the pauldrons [user customized, and they could get away with it for being so far from the States]. As DLC it would be an enclosed adventure ~possibly just a unique island, though it could have other options like a submarine or another Rivet City style settlement... It's easy to extrapolate this stuff.
If done well then I'd probably like it. I think the potential is there ~though easily missed, but it could be good if done well. I think that what matters is the people and the environment they create, not the actual location of the dirt underfoot.
That's my opinion.
*[Meaning their future equivalents not actual B-52's ~though maybe... why not?]