Well even if they do plop the 2.5L into a Corolla it wont be for a few years. They will wait it out until everywhere else in the world gets used to it then they will maybe put it into a corolla in North America. However, I think the smartest move and the more logical move for toyota is to supercharge/turbo the the 2.4L or 2.5L for the XRS model. I wouldn't put it past them to hold off on re-moding the XRS until next gen and then suping up a 2.5L to compete with the MazdaSpeed's & Cobalt SS's. But that may also be something they do with the Matrix aswell.
But this is all speculation. As for the original post... you can always get a 09' and then trade in once they release the new engine into the Corolla. I know I most likely will. Or I may also hold onto this one and do some custom mods myself once they become available.
Either way my 2 cents for toyota is to hold off on modding the XRS until next Gen and not just half-ass it and plop a standard Camry/Rav4 engine in there. Take the time and TUNE it so it isn't a glorified grocery grabber. Make it a fun sports model with better suspension/brakes/engine.