IMO this new Mustang will blow previous sales out of the water.
The base model ecoboost 305+ hp turbo 4 will be what the Honda Civic and Acura Integras were years ago so far as the "go to" car for tuning and customizing for cheap $. Some of the tuner mags are already saying that for only a few thousand in upgrades and mods, this car will be in the 400+ hp range from what they've found out. I remember the old turbo SVT Mustang was quite a car in its day with a turbo 4 as well, and it had around 1/2 the hp and torque this new one does.
I don't think Ford will abandon the crazy HP models like the Shelby line either, they just haven't released info yet. The 5.0 stats for the new one are still pretty impressive.
Again, I would bet that this new model will be a big seller, not just in Europe and overseas, but in the USA as well.