So, either the GTC class will essentially go away, or the GT3 cars will become basically GT4. Yeah, I see the GTC just "disappearing." That is, conforming to the Grand-Am GT3 specs.
This merger is weirdly timed. Because, wasn't it 2011 when Grand-Am, SuperGT and DTM sat down with FIA and all decided to conform to the FIA GT3 specs?
I will say, it will be nice to have two, better distinct, GT classes next year. GT2 and GT3 are great. Maybe with the combined series will see more makes getting in on it. Maybe McLaren and Mercedes will join up. Grand-Am, I believe, has already approved the SLS GT3 for racing, so the possibility is there.
EDIT: Approved Cars for 2013 Grand-Am GT Racing:
Aston Martin Vantage (Prep 1)
Audi R8 GRAND-AM (Prep 1)
BMW M3 E92 (Prep 2)
BMW Z4 (Prep 1)
Chevrolet Camaro (Prep 2)
Chevrolet Corvette C6 (Prep 1 and Prep 2)
Ferrari 458 GT ITALIA GRAND-AM (Prep 1)
Ford Mustang 2007-2010(Prep 2)
Infiniti G37 (Prep 2)
Jaguar XK (Prep 1)
Lamborghini Gallardo (Prep 1)
Lexus LFA (Prep 1)
Mazda RX8 (Prep 2)
Mercedes SLS (Prep 1)
Nissan 370 Z (Prep 1 and 2)
Nissan GT-R
Porsche GT3 Cup 2009, 2010 (GRAND-AM) (Prep 1)
Porsche GT3 Cup 2011 (Prep 1)
Porsche 997 “GTC” Spec (Prep 1)
Viper ACR Competition Coup (Prep 1)
For GX the Evora dropped out. We saw the Mazda 6 and Porsche Cayman
For GTSCC:
The Hyundai Genesis, Scion FR-S and Subaru BR-Z have all been approved for ST racing. Not many changes to the GS list.