Possibly awaiting significant changes to the GTD's CO2/km rating by making it run a little cooler to put less NOx out. R almost certainly getting a 10ps uplift and lower CO2 with the new 7 speed DSG (as per Audi S3) maybe the reason for delays to announcement.
... that could be part of it. Making big technology improvements with the GTE is probably the most achievable.
Maybe the GTI only requires small adjustments to give real world improvements.
Maybe the R and GTD are requiring more tuning to get near their previously quoted fuel economy figures, when using more realistic tests.
http://www.autoexpress.co.uk/97672/new-2017-volkswagen-golf-facelift-pictures "The new Golf will bring efficiency gains across its engine range - but the official figures for the car may only show a slight improvement as VW tries to produce data that can be matched in the real world.
VW’s head of development, Dr Frank Welsch, told Auto Express that his engineers would not be “pushing the limits” of how the cars are tested for fuel efficiency - and that this should give customers a better idea of what they can achieve in
regular driving. “We have
small improvements in the engines across the whole range,” said Welsch, “but as a result of the past year [Dieselgate], we changed the parameters and restrictions of our measurements on fuel consumption. We were all following these regulations - all manufacturers - but now we’ve made our tolerances even smaller
so the results are closer to the real world."
