The 13mm Rotor isn't really intended to allowed for 10.5 and 13.5 racing. It takes the "spec" out of it, and will create a motor of the month club. Or "Rotor Of the Month". This is exactly what BL is trying to stop.
The motors are externally identifiable, so tracks should be able to tech for this.
To answer you question, we don't ever intend to offer the 13mm rotors in any of the slower motors, and most likely not in the lower turn motors either.
It doesn't look like the 2.4 version GTB will in a combo.
Some guys have reffered to the SS GTB as the one that comes with an SS Pro Motor. I'm just trying to be as clear as possible.