Shimano never stops improving. Case in point is the Shimano Dura Ace R9160 Di2 TT Extension Shifters.
A refined ergonomic shape combined with Synchro Shift makes shifting faster and saves effort as well. Synchro Shift is a feature that allows the Di2 computer to choose the best front/rear gear combination whenever you shift with the rear derailleur. This eliminates the need to have two buttons per shifter, as now you only need to choose to upshift or downshift, and Di2 does the figuring out for you. Because of this, the 9150 shifters have only one button per side; one for upshifts, one for downshifts, and they sit at the end of each base. No longer do you have to move your thumbs to shift up or down, or even to move them off the shift buttons! And of course, Synchro Shift even eliminates the requirement for keeping track of which chainring you're in.
Since Di2 is customizable. You can choose which side shifts up, which side shifts down, and whether to shift one gear or multiple gears at a time.