The programmable shifting will be, IMHO, a great addition. I currently ride DuraAce Di2 with a compact crank. This after riding 30 years on my downtube shifting half-step+granny touring bike. That is going from a 4 tooth front shift to a 16 tooth shift. Heading into a hill, ready to dump to the small ring (34t) is where I notice the biggest drawback with a compact crank. That 16t change has me spun out until I lose mommentum, and I had come to plan a downshift in front and two upshifts in the rear to keep some kind of continuous force on the pedals. Being able to program in 3 shifts in the rear will be welcomed. There will still be a double shift required (front & rear) but now I won’t have to be double tapping the lever for the extra shifts. What will be really great is if the speed of the multi-shift can be accomplished faster than two mouse clicks.
And I do love Di2. I put Ultegra Di2 on my wife’s bike and she likes riding more than she did before. She was on Ultegra mechanical triple front and never could dial-in the trimming of the deraileur. Now with Di2 its shift and forget it. She loves it, really, really loves it.