WWE are not globally confident enough to take their PPV's very far from the USA. Canada being the only exception of recent times, Britain in the 90's and while they have been quite successful, I think it's a marketing risk WWE don't feel the need to take. I mean, why go out for milk when you have the cow at home, y'know? They know their U.S. based PPV's will sell out and the existence of Pay Per View sales totally does away with the need to take the product, literally, beyond their own shores.
And that goes double for the big enchilada, Wrestlemania. It's not about whether it would sell. There's no question that it would still sell out in certain countries.
I'd say, look for TNA to move into that market first.