Ooooh a game of guess the shimano road map my predictions:
-I’ll expect 10spd Tiagra Di2 2016-ish then,
-DA Di2 11 speed released about the same time.
-XTR Di2 11 speed for about 2017…
-All MTB groups down to Deore will be available in 10 spd Di2 by June 2019
Shimano will use firmware to dictate Shifter/mech compatibility based on a “+/- one group” principle, i.e. they might allow XT and XTR to drive one another, They won’t let Deore work with XT or SLX operate XTR, Road stuff will not work with MTB at all…
Various hacks will emerge in due course, and they might quietly drop the limited compatibility policy once OEM customers complain enough at not being able to mix Di2 groups as much as they could with the mechanically actuated stuff…