It is here (been out a couple of days) and it is a quite amazing piece of technology.
Shimano Unveils XTR Di2 M9050, Mountain Bikes Go Digital, Lose a Shifter
You can go single, but double and triple can shift front and rear with a single shifter! Self-align between front and rear, self-align in case of bent derailleur, programmable, according to the test runs (Lennard Zinn's first ride review of Shimano XTR Di2 - VeloNews.com) instant shifts better than any mechanical type. Huge range, of course wider than any single.
The future is here, although it will take a while to trickle down to XT or STX.
Shimano PRO Components Adds Di2-Integrated XC Handlebar, Stem & Seatpost
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Thread: XTR Di2 is out