I dunno if I would use IGH on a long brevet (a 3 speed on a 200 might fun). I've found my derailleur bike to be reliable enough and even if the shifters break or the derailleur gets smashed one could still shorten the chain and single-speed it. Also at PBP most of the controls have some mechanics you can pay, though I have no idea how many spares they'd have or what kind of experience they have but I doubt they'd be able to fix IGH issues... I had zero bike issues so no reason to talk to them. I don't recall seeing any of them swamped with people.
My hands were sore at the end of PBP from shifting so much, I run a 3x10 setup, that was when I decided I'd be open to electronic shifting. Seems like some of the ultra crowd are going that way. Cables are the weakest part of the shimano shifters IME, I just had to change out my cable after ~6000km on a brand new brifter, it had started to fray and would stop shifting onto the smallest sprockets, I was glad to get that warning sign before the cable broke. They are tiagra 4703, which have otherwise been a solid setup. I think Dura-ace jockey wheels having bearings, and maybe ultegra is bushing on top and bearing on the bottom? Not sure if I am remembering that or not. Tacx used to make some good bearing jockey wheels.