Car magazine were reporting that the Mk 8 is slated for a 2018 release, which means 2019 for the GTI etc.
Also, I can't see VW chucking in 320 horses into the Mk 8 GTI. The jump from the 6 to the 7 was only 20-30, and I'm pretty sure it was a similar jump from the 5 to the 6. I'd expect the Mk 8 GTI to have around 280-290 bhp.