"Prospect Magazine has invited 100 of the World's Thinkers to answer the question of what will define the coming century. Here are some answers, and as there are no bloggers in the Prospect sample, I have gratuitously appended my opinion at the last. Have a good weekend everybody.
...
Don Berry, journalist -- We need a planet-saving alternative to democracy. Mankind is set on exhausting the planet’s resources. Voters in rich nations will not want to give anything up; voters (or dictators) in developing nations will seek what the rich have."

Oh I got a planet-saving alternative, have nuclear war. The planet should do fine- and it will a final solution to Don's concern.

Another idiot said:
"Philip Bobbitt, political writer -- Nation state versus market state. The constitutional order of the nation state saw its role as one of regulating and reversing the results of markets. Market states, by contrast, try to use the market to achieve their governmental goals."

So we will have two flavors of socialism battling?
Nay, my prediction is Socialism dies with all those childless adults who dream of being a child forever. Next fad will be people who want a dozen plus children- having lots of children will be considered honorable and those with fewer or none will be seen as slackers.

Oh here is one with a slight clue:
Nicholas Humphrey, scientist -- How can anyone doubt that the faultline is going to be religion?

True, and so history repeats itself, over and over and over. But of course the question is which religions will be significant in 21 Century? Or another question is, what religion are most of the Chinese going to adopt [cause the Communism religion ain't going to cut it- though that might morph into a worshiping of a kind of formalized Chinese nationalism]. And I guess the other main question is will Islam reformation happen or will it still be happening by close of 21 Century.

And then added to the 100:
Wretchard, Internet diarist -- The Next Big Thing hasn't happened yet. But given a century in prospect there are significant odds that some contingent event, discovery or emergent technology will organize or divide us in ways we do not yet suspect. "Life is like a box of chocolates. You never know what you're gonna get."
http://fallbackbelmont.blogspot.com/2007/03/big-big-picture.html#links

Wretchard is probably right. Maybe something completely unexpected like world peace or something.