Well, considering it's sold almost a million already and outsold all home console versions of the series before, it is a success no matter which way you slice it, but it'll still be very disappointing if it doesn't do well outside of Japan. It's hard to say right now, but hopefully Capcom and Nintendo market it properly and push it well.
I can't imagine it selling less than 500k outside of Japan, so at the very least it should land around 1,5 million when all is said and done. With any luck and good advertising, it could hit 2 million.