I know Miyavi did a world tour and had fans everywhere he went. I can't help but think "if Miyavi can have so many fans around the world, why wouldn't Ayu?" but SunshineSlayer is correct. It's a big risk trying to plan a concert oveseas with the high probability of losing money.
Thinking of it that way, I don't care if she plans a concert in America or not. If she doesn't, oh well. I'd rather her not lose money trying to please her international crowd of fans. She still makes frequent trips to Europe/America and judging by everyone's experience when she was in London this past week, meeting her is not impossible or out of reach.
I really think there should be a Team Ayu ~International~ fan club. Maybe that way she can learn how many international fans she has. Which means if there are enough of us (which I know there are) she might plan something overseas for us.