Ford and the Thunderbird most recently parted on bad terms. The Thunderbird's most recent iteration became a heavy, ugly, slow attempt at a cruiser. But it wasn't always that way. The Thunderbird was something special once upon a time.
The Thunderbird was originally a big, heavy, handsome cruiser. While a direct competitor to the Corvette, Ford didn't market the Thunderbird as a sports car. It was more of a luxury car with a bit of sports prowess. As time progressed, the Thunderbird became bigger and more luxurious, then smaller and sportier. Really, it has been all over the map. The only important part of this abbreviated history was the first bit: it was originally a direct competitor to the Corvette. Ford needs that back.
As of late, the Mustang has been Ford's competition to everything. It makes it sort of hard to place. And in my mind it softens the nameplate because it is trying to be too many things. The base V6 is for people who want the look and badge. The base convertible is supposed to be a cheap sporty car for pretty much anyone. The GT is the modern pony car to compete with the Camaro. The GT500 is the muscle-y bruiser that can tear up quite a few cars from stoplight to stoplight. The Boss 302 and now GT350 are the hardened sports cars/track cars. Ford needs another car to fill some of these roles.
Luckily for Ford, the millennials that everyone is targeting probably won't remember most of the bad Thunderbirds. Sure they've seen them, they aren't easy to miss when it seems like all of the ones from the 21st century were bright teal. But bringing it back as a Corvette/Viper competitor would probably not conjure up the lump that it was.
Now for the tough bit. What drivetrain would be put in there? Ford is deeply in love with the Ecoboost, but the Corvette have old school American engines. A small-block V8 and a V10 originally based on a truck motor are a bit more appealing to the flag-waving mullet-sporting American in me than a twin turbo V6. Ford does have a truck V10 architecture, but it has never been a stellar performing motor. Then again, the Fox body Thunderbird had a turbo four. Ford's Modular V8 has been around for quite a while, and I feel like the V8's are nearing the end of their usability. The Coyote and Voodoo seem about as stretched for power as they can get. The GT500 had a bit more horsepower and could be seen as a direct competitor to the LT4 in the Z06.
The new GT is amazing. The Mustang does it's on thing well. But GM is beating Ford. The Camaro is doing everything the Mustang can do, but the Corvette is doing everything the Mustang can't. I think the GT is too far upmarket to be a direct competitor to the Z06, and it will probably be way out of the price range. Ford needs something, starting at about $50-60k with a performance model about $20k higher, to compete with GM. Hopefully if this happens, Fiat Chrysler will take up the gauntlet and make the Viper even more of a challenger. I think that there is a slight chance of all this happening with Ford's incredible doings lately, but I won't be holding my breath.