Someone was telling me about this the other day. Not sure I like the idea of button cells in the shifters. I like being able to recharge everything in one go.
You don't have to use the button cells. You can still wire up the shifters inthe traditional way and run them off the main battery. The 8170 and 9270 series levers can be used either wired or in wireless mode.
105 Di2 seems to be confirmed based on FCC certification for the wireless
https://road.cc/content/tech-news/shimano-105-di2-breaks-cover-293665
Weightweenies seem to have a pic