Future GT cars to use N/A flat 6?
 

A review of the Cayman 718, where they don't like the engine, but mention the future GT cars.
Maybe there will be a future Boxster with a flat 6 after all.

http://www.telegraph.co.uk/cars/porsche/porsche-718-cayman-review/

There has never been a Boxster GT car and I wouldn't hold my breath for one. The flat-six might remain in the next gen Cayman GT-4 but that's about all that I can envision. From here on out, its most likely all 4-cyl's for the Boxster.

Maybe the GTS or Spyder.

I don't think there will be a Boxster GT car, but if they can package it in a Cayman GT4, maybe the Boxster will as well in some form.