To interrupt the discussion and get back to the original question for a moment, using the new polyurethane tubes is a choice, like so many others we make.
Riding in the big-big combination is a user error. But I do it a few times a month, so I'll take the extra weight hit to make sure my chain's long enough to accommodate it.
I'll take a spare set of brake pads on a long tour because I've needed it. On a shorter, flatter tour, if I changed the pads last month, I wouldn't bother and would save that much weight.
I've looked ridiculous riding with the derailer cable's extra length coiled up because I didn't have the tool to cut it for a few days. But since I had the spare cable, I was still riding!
TPU on a coastal tour of the Gulf or southeast Atlantic coast? Sure. If you're worried about patching, take a butyl spare tube (or two).
Despite the entertaining techno-babble, I've personally seen and felt darn hot rims. (Don't feel them at the stop sign at the bottom of a 3/4 mile 8% grade!) And I've seen the aftermath of a couple of blowoffs caused by braking while touring. While some might immediately think, "User error!" my first thought was "There but for the grace of God go I." While I don't know the exact mechanics of how a rim blows when overheated, I can't see the tube weakening or melting at a lower temperature would be beneficial in any way. You might save a half a pound riding TPU tubes and carrying TPU spares. I'd think that was not a smart place to save weight on a mountainous tour. That personal choice thing again!