What are the advantages of Di2?
It seems disadvantageous to have to charge the batteries and move the entire bike to an outlet. What if the system becomes inoperable mid ride and you are stuck in 50x12 after a descent or 34x30 after a climb? Aren't the buttons too small for correct ergonomics (avoiding misshifts)?
Shimano's mechanical groups shift so well with so little effort already, how much easier does shifting need to be?
It seems like a solution to a nonexistent problem.
I can see how a wireless system would be advantageous by eliminating all of the clutter of wiring and cables, reducing rather than increasing complexity. Also, I think the batteries should be chargeable off the bike.