There are rumors that the TT will be ended in favor of the "new Audi quattro".
It would be based on the MQB platform to take over the TT slot in the Audi range, because the TT is not making the number it should be.
The "quattro concept" (very well liked) is not that much bigger then the TT Mk2 and the TT Mk3 would grow anyway, making the differences less then 10 cm wheelbase and overall length.
The "New Audi quattro" can be put higher up the Audi chain because it's more exclusive then the TT.