I was just about to check up on this myself. SuperGT isn't going to be the only race series to ge the Ford GT. Take a look at what is being featured over at Speed World Challenge.
Pic of the SuperGT GT...
Speed GT
Aston Martin DB9
Audi S4 (TT) (-2002)
Audi RS4 (2006)
Audi RS6 (2003-2004)
BMW M3 (E46, 2000-2005)
BMW M3 (E90 2006-)
Cadillac CTS-V (2004)
Chevrolet Corvette (C5, 1997-2004)
Chevrolet Corvette (C6, 2005-)
Dodge Viper GTS (-2002)
Dodge Viper Comp Coupe (2003-)
Ferrari 360
Ford GT
Ford Mustang (2000-2004)
Ford Mustang (2005-)
GM Firebird/Camaro (1993-2002)
Lotus Esprit V8
Lincoln LS-8
Mazda RX-8
Mitsubishi Evo 8
Morgan Aero 8
Nissan 350Z
Nissan Skyline GT-R Z-tune
Pontiac GTO
Porsche 911 (996, 1998-2004)
Porsche 911 (996, 2005)
Porsche 911 (997, 2006)
Porsche 911 (AWD, TT)
Saleen SR351 (1999-2004)
Subaru WRX STi
Volvo S60-R
SPEED Touring Car
Acura Integra (1994-2001) 12/8/05
Acura RSX-S (2002-) 12/19/05
Acura TSX (2004-) 12/19/05
Audi A4 (B5, 1996-2001) 12/8/05
Audi A4 (B7, 2005-) 12/14/05
BMW 325i (E90, 2005-) 12/9/05
BMW 325i/325Ci (E46, 1999-2004) 12/19/05
Chevrolet Cobalt SS
Dodge SRT-4 12/19/05
Ford Focus Coupe 12/8/05
Ford Focus Sedan 12/21/05
Honda Civic Si (06-)
Honda Civic (03-05) 1/4/06
Honda Civic (-02) 12/8/05
Lexus IS 300 (2000-2005)
Mazda Protegé (1999-2003) 12/8/05
Mazda 6 1/4/06
Mercedes C230 (2002-2005)
Nissan Sentra SE-R Spec V
Subaru Legacy GT
Subaru WRX 12/8/05
Volkswagen Jetta (Mk 4) 12/8/05
Volvo S40