I'm replacing my Fuji Touring frame with a Soma Saga frame. (Explanation to wife: I'm not getting a new bike, just replacing a component or two). I'm transferring most of the parts to the new frame, but I'm taking the opportunity to upgrade a few things in the process.

I don't tour in 3rd world countries. Since I do almost all of my own build/repair work, I feel confident fixing or getting along with just about any failure I could have on a tour, given available tools and parts. I won't start a tour with obviously worn tires or worn out components. Therefore, I evaluate the possibility of component failures on tour as catastrophic (can't ride, must walk/push, or worse) or inconvenient (fixable or a rideable "limp mode" exists).

For example, I'm finally ditching the bar end shifters with a friction option for Tiagra brifters. I love the STI shifters on my other bikes and they've given me many miles without failure. If I do get a shifter failure that I can't fix in the middle of nowhere, I can always engineer a bit of cable hacking or fool with the limit screws to lock the front or rear derailleur into a middle fixed gear. That gives me either a 1x9 or 3x1 drivetrain, depending on which shifter is broken. That's certainly good enough to get me to the next bike shop or even complete my trip if the terrain is suitable.

Square taper bottom brackets and their associated crank arms can potentially be in my catastrophic category, although very unlikely with proper tightening and maintenance. The square hole in the crank arm leave 4 high stress points in the corners, but manufacturers engineer in plenty of metal to compensate. Over-tightening, under-tightening, or riding a loose crank arm is bad news, but generally avoidable.

Splined crank spindles are a much more secure interface to the crank arms. I'd place them in my inconvenient category of failure because just about the only bad thing that can happen is bearing failure. In that case, you typically get lots of warning that things are going bad and, especially with cartridge bearings, they may complain loudly and roughly, but they continue to be rideable to the next bike shop without destroying anything else.

I go a step farther for myself and prefer the modern outboard bearing bottom brackets. I'm a pretty big guy and not at all sensitive to requiring a narrow Q-factor. The outboard bearing bottom brackets combine the splined (or permanently attached) interface to the crank arms with large, supportive bearings widely spaced for good crank spindle support. They're drop-dead easy to install and require no adjusting. If anything does fail on a tour, the next bike shop will almost certainly have the parts and knowledge to get me going again.