Greetings Madhatter,
I was surprised when I was at the dealer open house, I got a really good chance to sit in the new seats.
My 2015 gc1715 seat I have and the new seats they now have are the same including the coils and spring suspension (color and storage pouch are different of course). But recognize the bracketing of the new swivel seats on the gc1710 is different than the former. So when I sat in the new gc1705 I could notice some difference with the new steering wheel. But I was a little surprised that the new gc1710 and gc1720 have a different height of the entire seating position than does the gc1705 and gc1715. Maybe I didn't notice it in the prior gc1720 because I don't have one but I noticed it in the gc1710 for sure because the new seat is that nice firmer comfort that doesn't squash down just like my gc1715 seat.
I noted with the new steering wheel and new seat combination that my arms had to reach further on the 10 and 20 because the apparatus under the seat for swiveling raises seat height. Just something for you to notice next time you are in the dealer.
I also specifically asked about the couplers as visually they are larger. They told me Massey found the couplers created a resistance point compared to the hydro lines, and when the couplers were changed, it allowed the hydro pump for the fel to transfer more fluid faster without changing the pump or lines. My guess is pump pressure stability either way but flow volume could improve especially for quick initial movements that are common with a fel.