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and, regarding points 1 & 2, everything is obsolete these days. If you want to wait for something definitive, you'll be waiting a long time. Discs are only new on road bikes, they are c. 15 years old on MTB, and a pretty mature / stable standard. And if you're worried about maintenance, get cable discs. For all @edscoble 's snobbery, they really are pretty good, and are a very simple system to set up/maintain
my hesitations over discs are that
(1. whatever I get will be old-hat and surpassed by something better within 6 months
(2. They'll cause issues in r.e. to maintenance - I'm an absolutely terrible mechanic at the best of times and standard calipers are just about doable for me currently!
I guess I could always go for the DA Disc version OTP, I do fancy electronic though.
If you went for frameset only and bought di2, would you need to purchase different shifters for discs?