RustyC

I think there are a number of scenarios where fuel makes travel less and less affordable. Some of the dark "peak oil" scenarios throw us back to the 19th century, with steam engines the main hope for long-distance travel. There would definitely need to be a technological game-changer in there to keep affordability going. If they ever get the A380 out there it could continue the 747's game by flying more people at lower per-person cost, countering some of the effects of rising fuel.

Just as important as those issues, though, is the threat that increasing homogenaeity poses. "See the world...while there still is a world to see." What that means is that satellite TV, movies and other cultural exports, multinationals and others are stripping a lot of the uniqueness from places. McDonald's replaces mom and pop eateries. People don't live in "traditional" houses for their area anymore. Four or five giant media companies own most of the satellite channels. Tourist sites get mobbed. Consumer culture takes over everywhere. That "shrinking world" problem means there's less of a "there" there, and that could be just as important as the cost problem in discouraging travel.