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Any theories as to why not?
Shimano philosophy. They won't release wireless just because the market demands it (in spite of their unconvincing protestation). It will have to be better than Di2 in some way beyond just getting rid of the stupid bird's nest of wires and junction boxes, it will have to be indigenous (Shimano really hate paying licence fees), and it will have to be portable to Ultegra at least, and ideally 105, which means it has to be producible at a much lower price than eTap
Any theories as to why not? To be completely honest, I've never really been impressed with Etap.
In it's short availability, I had more come in needing some sort of adjustment/attention than Shimano's offering.
I know Patents aren't really an issue, but is it something to do with signal protocols? reliability?