Shimano has dabbled in road disc for a while, but always at lower levels (RS-505, RS785, etc...) than their haloed Dura Ace level. They took their sweet time coming to market, several years after SRAM first launched their HRD groupsets. While late to the party, Shimano has really come in strong with a groupset fitting of their pinnacle road product. Whereas other road hydraulic hoods (including their non-series R785) look unsightly and feel ungainly, its the 9170 levers are so sleek that its difficult to tell that they house hydraulic master cylinders. The lever blades are (from what I can tell) a carry over from 9150 series Di2 rim brake, but are reshaped from the previous gen to fit your pointer and middle fingers just perfectly when in the drops. The Di2 shifting is unremarkable in that even from previous generations it shifted perfectly, every single time and even under load. FWIW, I unscientifically feel that Di2 shifting in its standard factory setting feels faster through the gears than Etap HRD does.
Finally, the braking: I'll be the first to admit i've been pretty curmudgeonly about the whole road disc movement... I consider myself a fairly capable descender and have never melted carbon rims or anything of that sort. Disc brakes will inevitably be heavier, so what gives, right? In a word, performance.
I really shocked at how much better of a descender i was on disc brakes. Whereas on a rim brake bike with carbon wheels I'd have to start braking pretty early and hold firm pressure throughout the corner to scrub speed, i found myself testing how late i could hold speed and brake going into corners due to the far superior braking power. Just as important as the actual braking power was the confidence in which I knew that it was there. Everyone has experienced that feeling while riding carbon rims that you're just not quite sure if you're going to get the braking you need. I know for a fact that you'll be a faster descender on this one than your current rim brake bike. I was one of probably 20 or so riders in the Pinarello Gran Fondo who had the privilege of previewing the F10 Disk early, and found myself flying past other F10 rim riders while descending. This day happened to be perfect weather, but in wet weather the advantage of disc brakes is so much more pronounced.
Make the switch to disc. Unlike previously, you won't be making any compromises.