I think what may ultimately spell the end for Di2 is the fact that they're selling an electronic assist to a crowd that prides themselves on human powered transportation/propulsion/etc.
Most serious cyclists have embraced technology in the form of materials and mechanics, but have shunned technology that involves electronically powered moving parts.
I think that's why the same crowd that drools over carbon fiber, and owns cycling computers, and a whole host of "space age" componentry responds so negatively to electronically powered shifting.
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