Originally Posted by
atwl77
You missed the point, it isn't about frequency or reliability. It's about what you can do if it fails. In my example above, several experienced people at the controle couldn't figure it out. A friend of mine recently had connection issues, messed around with the thing and eventually took the bike to the shop to get it rectified. I don't need this kind of stress during an ultra endurance ride. With a mechanical derailleur, all I need are spare cables (you bring them on 1000k and above, don't you?) and tools and I can fix 99% of any issue that comes up.
Likewise with tubeless. Sure they generally work. But on the rare occasion that they don't seal, I don't want to deal with putting a tube into a messy gunk-filled tire in the middle of an event, and also deal with mounting and unmounting tighter-than-usual tires in the process. And yes, a couple of people I have ridden with had exactly this problem - punctures that aren't sealing.
That's a valid point, but I think it's a bit more nuanced. If a Di2 system is less likely to malfunction (e.g., because there are no cables), then the ease of repair is less of an issue. And, for what it's worth, the last couple problems I've had with my mechanical drivetrains were not so easily repaired.
I also suspect that, as electronic drivetrains become more common, then more people will be knowledgeable enough to handle the occasional problem. But perhaps we're not there yet.