Suggesting it would sell less means you can only believe the Wii is selling well due to the lack of supply. And if this was the case, there'd be a lack of supply for all consoles, since the others could use increased sales too.
That's a very silly viewpoint.
It's hard to say how well the Wii would do -- it's a self advertising system. You hear countless stories about how people take their Wii to a family gathering and 5 more people want to buy the Wii. Because this is the case, every Wii sold is more potential advertising. The kind of advertising you can't do on a TV.
The Wii would be doing much better than now, that's the only thing we can say for certain.