The difference is that when Apple introduced both the Retina MacBook Pro and the non-Retina MacBook Pro in June of 2012x they both had the exact same hardware specs (CPU, GPU, max RAM) providing users with a bridge device that had some of the old stuff (FW800, GbE, DVD-ROM, HDD, BTO SSD and matte display options). At that point, the only substantive difference between them was the slimmer chassis. I believe the keyboard mechanism may have been slightly different.
My point is that if Apple is moving away from the ID of the current MacBook Pro to not admit the issues with the current model, they will use the larger 16” screen to justify a thicker, “more robust” chassis with better cooling and revised scissors mechanism to help save face. I expect they will want to have 10nm 45w TDP CPUs, LPDDR4, in there to go to 64GB max, Navi 7nm GPUs to 8GB GDDR6 and a larger battery. Doing this sort of radical change will allow them to jettison the 15” model immediately and distance themselves. They want to do that after they have gotten all the mileage out of the 15” that they can, warts and all. As soon as the 16” chips, the 15” sales will drop off a cliff.
Ice Lake H-series won’t be out this year and unless Comet Lake H-Series (10 cores, 14nm) actually ships, I cannot see Apple settling on using the 9th Gen CPUs they have already used, because they want and need to distance from the current 15” to prevent customers from having any bad associations they may have now.
Unfortunately, no, I strongly believe the 16” is a Q4/2020 or Q1/2021 product, depending on when Intel ships the Ice Lake H-Series.