The infrastructure for trains is already there (China -> Europe), its just static and therefore inflexible. It isn't going through politically unstable areas, just Russia. As long as you don't bet on one horse you're going to be fine. I don't know anything about trains from Africa to Europe. I believe China exports more than Africa.

Since we don't talk about last mile, they're competing with ship and airplane. For last mile, there's only the minivan/truck solution, though I'm not sure how widely adopted or sustainable drone delivery is as of now. A low carbon footprint of drone delivery would be a plus for adopting it long term.

A blimp still needs to cross those areas, and could be shot down