We all know VW as most other manufacturers are launching new models much earlier than in the past. We know the Mk6 was effectively a heavily facelifted Mk5, plus the different 2.0TSI engine etc.
Total guesswork but the Edition 40 (I'm sure there will be one) should be here in 2016, so Mk8 GTI likely to be 2017 only fours years from now.
The MQB setup will certainly be around for at least 10 years, so will the Mk8 be an evolution all be it predominately a face lift of the Mk7?
I wouldn't be surprised to see 'unofficial' pictures two years from now

Point is when is a shelf life of the latest GTI too soon to change again for the next incarnation?
It's all a bit Doctor Who
