Thinking about Di2 and other e-shifters, and the frames designed to accommodate them. If one were to get a custom frame built around such a system, how much will obsolescence of the tech or changes in the mounting/routing change over the course of years? On a custom frame, one wants it to last a lifetime (or as long as possible), so what are the chances that a Di2-built bike will fail to accommodate a later incarnation? Or is the layout of the hardware pretty set in stone at this point?

I wouldn't worry about that. There are lots of Di2 equipped bikes that will be supported for many many years. Probably the only major change you'll see if cableless shifting and that won't affect anything.

Thanks. I'm interested because I'm disabled, minimal fine motor control on the right side. Since the right lever controls the rear mech on Shimano and can't be switched, I'm always at a disadvantage. I heard that either lever could be paired to either mech with Di2, so I'd set it to left/rear.

Have you thought about the Alfine Di2 with the flat bar shifter? It is just a press of a button and it shifts.

The only one concern I might have is if they increase the rear cassette to 12 speeds. At some point they will have to space the rear drop out to get in more gears. I already have a friend that has gone to a 1x12 on his MTB. Though the 1X12 still works on a normal frame if that frame has 135mm spacing. But that isn't the case with a road bike so as long as they stay with 130 mm DI-2 or E-tap should work.

That's an option too. I like long distance riding in variable conditions, so I had my eye on a Rohloff Speedhub. For the touring, that's not a bad way to go regardless.

Yeah. I don't ride road hard enough to need elite-level speed on shifts, so mechanical IGH is enough, but for the 'cross bike, I'd prefer my investment to go for a little while. If I could get 5-10 years out of a system or bike, I'd be happy, cause I put a lot of miles on.

Does anything support flightdeck?

Standards can change quickly, although there seems to be quite a few Di2 devices, so perhaps Shimano will choose to keep everything backwards compatible, for some time.

Oh to be forcing replacements be bought like computers and phones do..

simpler, mechanically, the less to go wrong and be un replaceable.

Wireless electronic shifting, such as SRAM's is less dependant on frame design.