Yes, an STi tuned wagon is availible in Japan...and as a gray market import to many other European countries. It is very unlikely that it will make it to the U.S. through Subaru dealerships...that's not to say you couldn't have one imported by one of the gray market importers here!
I'm hoping that the US demand will lead them to importing the STi Wagon, but it doesn't look good for now!... If anything it'll probably be after the first allocation of sedans are sold out, but I don't think I can wait that long!! My current ride's fading fast!!