Didn't see this updated here, but in a Zinn article around June 10ish (sorry, screen-reader won't let me jump back and forth) he mentioned that his original comment about the DI2 XTR triple wouldn't work with road shifters was a "brain fart" and at the time he was thinking mechanical shifters... A further email quoted from Shimano clarified that the FD will in fact work with road shifters but the road chainrings were outside of size spec for the XTR component.
Update:
Still can't put in the link, if you search it out this is buried in an article about biopace rings among other things...
"
Dear Lennard,
When you say there are not enough clicks on a Di2 chainring lever to shift a triple, what does that mean? I’ve always assumed that Di2 levers have two buttons — up and down — and I got the impression the newest versions will just keep shifting until the derailleur runs out of gears. Is this not true?
— Steve
Dear Steve,
Yes, it’s true. That was a brain fart on my part. I was speaking as if it were a cable-shift lever.
You could run the XTR front derailleur on the XTR triple crank with an Ultegra Di2 or current Dura-Ace Di2 lever. Shimano has made it possible for some time to reprogram the levers so that the right lever shifts the front and the left lever shifts the rear. So obviously, there is no limit on how many gears it can shift other than what the derailleur is limited to.
Here’s an answer from a Shimano spokesman to the same thing:
A reader asked about installing the XTR Di2 on a tandem for use with a triple. If the reader used the XTR M9000 triple crank, he/she would be able to actuate that with a road Di2 lever using the new XTR Di2 M9050 front derailleur. Unfortunately, if he used it with a standard road triple, he would be outside the Shimano recommended compatibility parameters. Though it may be possible.
― Lennard "
Copied from a Velonews article.