I just don't see Ford going to the trouble to import that model - they end up with an "orphan" model in the middle of the Focus lineup, nothing like the rest of the cars, which shares few if any parts (I mean not even body parts, which at least the SVT version did). They would have to maintain a stock of parts that wouldn't interchange with any other Focus, just for this one low-volume specialty car.
And on top of that it would have to be legal for sale here, which means it would have to go through the whole process of crash testing and emissions testing, and receive yet more "orphan parts" in the form of North America-only bumpers, lights, and related parts - special parts for North America only, for a car that's only going to sell a few thousand copies a year. Not to mention then you leave the salespeople with the burden of having to answer "why don't all the other Focus models look like this one?" over and over again.
Take yourself back in time to the '90s - can you imagine if in the middle of the North American Ford Escort range they had also offered the European-model Escort RS Cosworth? Sounds pretty ridiculous, doesn't it? The only thing they would have had in common would be the name Escort. Same idea here.
And as many have said before, including myself, no way is Ford going to undercut Mustang sales... have you seen the 2005 Ford sales figures?? The Mustang is the only car Ford has right now that is actually selling well. No way in hell are they going to jeopardize even a slight reduction in the sales of that cash cow.