I disagree. when you break the game down, each area only has a few screens, some of these are reused at different points in the game, some of them are made longer by having dead end paths or exploration routes. It has many seperate locations, but no more than something like Skyrim. I replay the game every year or two, and can see no reason it would be difficult other than already mentioned. Because they are going to make 1 area the equivalent of 10 screens to move through and fight on, and this is the issue. They could easily rain that in. But they won't.
The game does not at all have more content than current RPG's. The difference is this is SE, so they will spend 2 years and half their budget on cut scenes and flashy shit, then wonder why it's so much work to make.
Yeah I think it can be done in one release no problems other than time. I just don't think MMO's are a good basis for arguing volumes of content, because they NEED to have a lot of content to keep players subbed.