Bernie will not allow Indycar at COTA, or even in Austin. This sounds like maybe Bernard is looking for a way out of TMS.
Why wouldn't Bernie allow IndyCar at COTA?
It gives people a straight up comparisson of F1 and IndyCar. The last time this happened was CART (I know that's not IndyCar, but close enough) and F1 raced in Montreal in the same season. Minardi's lap times were seconds quicker than the CART pole.
If you like IndyCar, you'll love F1. Bernie would probably love for everyone to compare IndyCar with F1 and see which product is 'better'.
ALSO, it's a common practise for major sporting venues to do a 'practise' event before the big one just to make sure everything works. If Randy Bernard can demonstrate the total lack of hotel space and road access at COTA before the F1 circus shows up, that's one less black eye for Bernie... he can simply say the organisers were aware and didn't do anything about it. (Isn't that his standard line for Silverstone?)