Shimano, keep updating the firmware to improve functionality and add new features, although I have never experienced a better performance once I update, it has always worked flawlessly. The new features like being able to use XT/XTR derailleur combo with 6870 Di2 hydro shifters is a new update a few weeks ago, my new bike has this setup. Syncro-shift is, I believe a one finger function where the front and rear derailleur will simultaneously changed to move you onto the next appropriate ratio, so if you cross chain big/big the next change will alter both front and rear to next nearest ratio.
The other function which has been out since Di2 became available is multi-shift, where you hold the button and the rear derailleur will travel the cass rapidly
Here is the news re Phone firmware updates
http://bike.shimano.com/content/sac...mano-advances-wireless-di2-functionality.html
You will need the new bluetooth battery to make it work, I got this on my new build but still choose to plug in my PC and use the SM-PCE1 to update and configure the shifters.
Edit Ive just updated my bikes, the road Di2 6870 updated, I couldn't see anything to do with syncroshift. My MTB/Road Di2 updated the BT battery and then I had option to choose ratios in a setup table. It asked for front chain ring and rear cassette ranges and then listed the overlap ratios. No mention of synro-shift again, I'll go for a ride shortly. So it looks like on first impressions that the battery is the item and needs to be BT version. I'll do some more investigating.
Edit 2 No syncro shift on either bike, I think I need the XT/XTR bluetooth thumbshift adding to my combo bike. Cant be bothered with that at present, hopefully more updates in the future