In principle, anyone can luck there way through a cup competition. It hasn't really happened in the World Cup yet, but it wasn't long ago that we were seeing Greece pick up the European title. And never underestimate FIFA's willingness to use corrupt referees to favour the home team (*cough*Korea*cough). So given that, I could see Russia having a good go in 3 years.
I don't get this obsession with the USA and China. People assume that big population + money = World Cup. Which is how it works in the Olympics. But football doesn't work like that. It takes decades to get the infrastructure required to reliably produce the sort of talent capable of winning a World Cup. China has a barely credible league, where corruption and match fixing make it somewhere no-one talented wants to work and a horrible environment for young talent. MLS is growing fast, but it's still not yet in a position where it's regularly supplying decent players to the top European leagues. Maybe every few years someone will emerge that's capable of playing for a mid-table team in England or Spain. But have they ever had a genuinely world class player in the same way that relatively small countries like Sweden, Croatia, Romania or even Wales have, not to mention countless African countries? They spend a lot of money bringing big names into the squads, but are they spending the same sort of money on bringing in the best coaches to train their own youngsters? And are the most gifted kids actually playing football, or are the kids who play football still often the ones that couldn't get on the basketball team?
Any country can pump shitloads of money into a minority sport like, well, pretty much anything China wins a medal in at the Olympics, and get results. But it's much harder to do that in a rich, highly competitive sport that pretty much every country in the world takes very seriously. And there's no sport on the planet that's more competitive than football.
Anyway, I'd say that obviously the Netherlands, Portugal or Belgium would be the most likely to win it in the near future. Longer term, I think Russia are a decent bet. Poland have produced a few good players and if they continue to do it, they might have a world class team one day, with that population. Turkey are far from their best nowadays, but they've definitely got the potential to have a very good team at some point in the future. The European teams are always going to be at an advantage, with easy access to top quality opponents. With the likes of Nigeria, Ghana, Cameroon and Ivory Coast, they always produce 2 or 3 world class players at any one time, but they never seem to be able to produce enough decent players to fill out the rest of the team with the CL quality players that World Cup winners usually have. I kinda get the same impression from teams like Colombia and Chile. They're always going to have a few world class players capable of causing a few upsets, but the rest of the squad might be Championship standard.