Originally Posted by
mtseymour
First of all, I'm pretty sure that you'll love the improved shifting from 2x11 Di2.
Before you mix road shifters with XT Di2 rear and front derailleurs, check that Synchro Shift will still work. If my memory is correct, the E-Tube software doesn't allow a mix of road and mtn Di2 components to setup Synchro Shift. Once you select "Road" setup, it will only offer a list of compatible road Di2 components.
You should also consider the new Ultegra RD-R8050-GS rear derailleur. It can now handle a 11-34T rear cassette. If this is still not low enough, you can always get a Wolf Roadlink for a 42T casssette.
You can absolutely mix road and mountain bike components together now. Our adventure Calfee tandem has Ultegra Di2 road shifters and XTR front and rear derailleurs and works flawlessly. I use a XT display on that bike for wireless updates etc. Our road tandem has full Ultegra Di2 with a XTR display and again no issues and they will both do synchro shifting. I have not tried with a different junction box however just the XT or XTR display ones. We have been using the standard ultegra rear derailleur with a Road link or K-edge cage for 11-40 for a couple of years without issues. Also be aware that using a XT front derailleur you need to use a xt rear as at this point you can not mix derailleurs. Also the mtn front have chainring limitations. Both mtn and road shifters are merely switches and are not smart.