Originally Posted by
FlashBazbo
merlinestraligh, what do you mean by "sequential shifting"? Di2 already has sequential shifting, as I would define it.
One shifter controlling front and rear derailleur. Up, it goes to the next highest gear combination, shifting rd alone, fd alone, or a combination of both FD, RD based on what the next ratio is in the sequence, and Down it goes to the next lower ratio.
A Bike shop at Interbike, hacked a Di2 setup to do this on a MTB. Apparently it's a pretty easy program change.