Ford is probably using it to test people's reactions to it before releasing it. With all the rich history of Mustang names/variants, I can't imagine Ford would result to something as obvious a Nissan ripoff as "GTR"--especially with all the (justified) ridicule Mustang owners get for putting a GTR badge on their cars. I personally want to see the production vert.
Does anyone have a subscription to see what the article says?
If the regular V8 car is GT, then there is nothing wrong with GT-R for the higher perf version. I'm sure Nissan isn't the first car company to use that designation.
If it's got the performance for the right price, I'm sure there will be plenty of people snapping them up while the traditionalists piss and moan about the name.