This is the 4th version of electric shifting for Shimano, it's going to be years before the other brands are able to refine and innovate like Shimano has, perhaps they never will.
The mechanical component upgrades can be seen on our post here: Shimano Dura-Ace R9100
The new Dura-Ace 9150 Di2 group still has wires like before, it's no surprise to see Shimano play it safe in favor of performance and reliability and not follow the early break into wireless. Di2 as we know it might well be the most reliable of all groups on the market. The new 9150 Di2 does however have a number of innovations not seen before most notable synchronized shifting which is a programmable option. You can chose to have the system auto shift the front chain rings based on chain position in the rear or you can program it to shift to the optimal rear cog based on the front chain ring selection. We imagine most professional riders will still go full manual but time will tell on this one.
The junction box is now available in three versions and can be hidden in the frame, handlebar or the traditional under stem mount.
Some part of the new system is wireless the EW-WU111 wireless transmitter unit, in combination with two new battery options allow connectivity to iOS and Android devices. With use of Shimano's free app and the Shimano power meter it promises to be the ultimate system for any high end road machine. Finally a fully programmable system that's user friendly.
The new Dura-Ace R9150 Shifters are made for both mechanical rim brake and hydro disc brake with a very similar shape to the current Dura-Ace but a enhanced "mechanical like" feeling shift button. Shimano have also made an update to the mechanical brake actuation and the new lever is reported to have lost the dead sport right at the beginning of the lever pull.
Overall the group weight goes down but it's not significant. The overall weight of the Dura-Ace Di2 group has traditionally been the only negative we could find about it and seems this is unchanged.
Shimano Dura-Ace wheels also got a big upgrade. Read more here.. Shimano Dura-Ace 2017 Wheels
We have group prices and weights see here: Shimano Dura-Ace 9150 Groupset Prices