I think the thing in STi/Ergo vs downtube shifters is that the benefit is a clear, easy to show one. I'm not sure you can say the same of electronic vs mechanical shifting (via STi/Ergo).
I could be wrong, of course, and auto indexing/auto trimming is what the world's been waiting for, but I can't personally see the appeal, and can't imagine going out of my way to own an electronic system. Cables have a fair advantage and appeal for the amateur, I think, in a way that reducing the control of shifting to black boxery simply doesn't...