Primarily ease of international/remote welding or bending if the worst were to happen!

Honestly though, even remote parts of the world are growing more accustomed to travelers with aluminum or carbon frame bikes, it's becoming less and less of an issue.

I think someone would be just fine with another material, if they had a strong preference! The engineering of modern bikes, no matter the material, is amazing these days.

What's your ideal bike for touring?