TESO most likely will have A LOT of problems on release, just by doing 1 server only, so everyone will be on one server could lead to major crashes and lag issues, even with skyrim the game will still crash when triggering certain things, like doing a quick save during this one quest (forgot name of quest) will cause the game to crash, and that has been like that since the game came out no hot fix on it or anything.

I can't imagine how it would be when 10, 000 people go to one city at once? providing they have a huge player base like that, but yea everyone on one server O_O.