Hydraulic shifting has popped up several times over the last three decades but it has never taken off. I suspect that electronic shifting will become widespread within the next decade.
I just had a quick google around, and 5rot seem to have been the most recent to do it, four or five years ago. I guess like many things in bicycles, it's been invented over and over again, and eventually may take off. Things like clipless pedals, shaft and belt drive have all been "invented" umpteen times, although clipless pedals is the only one of those three to significantly succeed.
As you say, electronic shifting is very likely to have most of the advantages of hydraulic shifting, without all the faffing about with seals, and the potential for leaks. Once it's been used enough in the pro-racing teams, and the rich early adopters, hopefully it'll filter down to us mere mortals, who don't want to spend several thousand on the gear changers alone! I really like the idea of a self calibrating changer.
Of course electronic shifting would also have massive benefits to recumbent and tandem cyclists, where the long cable runs often make their changers even less reliable than those on more conventional bikes.
