International football will die out within the next 50 years.
This is just my particular prediction, and it's quite possibly skewed by the fact that I've never been a fan of international football, but I see there being a progression along these lines:
Within the next five or ten years, a player at Barcelona (probably, they've probably got the strongest "club culture", making them prime candidates) will declare himself "retired" from international football before he ever actually gets a cap, probably at about age 17. It'll be someone like Eto'o, a bloke from a poor footballing nation, who knows he'll be several cuts above anyone else who he'll ever play with internationally. Someone from Namibia, or Estonia, who'll be lauded as "the next Messi", and he'll be persuaded by whoever the Barca manager is not to bother with internationals, and just to focus on representing Barcelona.
That, in my opinion, will signal the death knell for International football. More and more players are already retiring younger and younger to prolong their club careers, and once the first "high profile" player declines altogether, loads will follow. Guys who just don't care about "representing their country". There's already very little prestige in playing international football, and the likes of the English guys who play for Scotland won't bother anymore. In the end, you'll end up with it being the second tier of players from some nations (for example, Australia's European based players all basically pack it in because the travelling isn't worth it), and gradually the rest will follow suit.
It's just my opinion, and it might not be unpopular, but that's what I can see happening.