My touring bike is a 3 by 8 with friction shifters... parts availability is not an issue and when I upgrade my wheel set will run a 3 by 7 drive with a freewheel on custom hubs.

8 speed parts are still readily available as are freewheels and good friction shifters are pretty bulletproof... my derailleurs date to the mid 70's and could be replaced with any classic model with the right capacity as well as any modern derailleurs.

I think that a modern touring bike with a 9 speed system would be more problematic to maintain in remote areas...with a friction system there are a lot of options when it comes to repairs if you are in a pinch whereas finding brifters or indexed bar ends might be a little tougher or require a wait.