I'm down for it. I'll most likely never own a set unless I buy used in about a decade, but I think it's cool as hell.
I would guess, and it's totally a guess, that Tiagra and lower will remain mechanical but will eventually move to 11 or 12 spd in the rear.
People that get 105 and up group sets tend to ride more and will see the benefit, while often time Tiagra and lower aren't ridden as often and battery charging becomes a detriment.
Unfortunately, this may effectively signal the end of advancement for mechanical drivetrains from Shimano.