I think for my mind clutch is the main reason that would stop someone from going from a GS car to STH, especially if you have a 6MT. We know DSG is more robust with extra power added, while 6MT can barely survive on stock level.
The change though I doubt will just roll through it though. If you think about ST classes in general a clutch allowance might not mean a whole lot in STS/STX or even STR. But in STU or STH it might shift the balance, considering I'd imagine an AWD car might be limited by clutch as a driveline fuse to get more power, especially now that boost is no longer limited.
On the LSD thing I think they can add a LSD if they don't have one(I don't know any AWD car that doesn't have one, and Haldex coupling is viewed as a LSD), so if they added another LSD its definitely illegal.
On the TCU tune I wrote a letter a long time ago about it and it was not viewed as good for the class. I still think its really no different than having a ECU tune in most cases. I say keep writting letter I guess. But only VAG cars really care about it....
