I don't think that Chinese will ever become the worlds lingua franca like English today.
Mostly because Chinese is not widespread enough. It's basically only spoken in China and there aren't enough people who speak it either.
Even though all 1000 million Chinese spoke the same chinese (which they don't), it wouldn't be enough.
Just consider the following figures. (they might not be a hundred percent correct)
There're about 500-600 million native English speakers.
Add another 400 million Europeans as they'll never accept an non european language as the official lingua france (and the've already chosen English).
Add 1000 million Indians as they have already opted for English as the offical language.
Add 400 million south americans. Their culture is too close to the European and American.
So they'll probably never pick a culturally totally different language as an official lingua franca (and English it's easier to learn for Spanish speakers anyway).
Add another 500 million Africans (probably more as the population there is likely to explode in the next 20 years)
Add some 100 million in south-east asian countries which have already chosen English as official language (e.g. Phillipines, Singapore)
This results in roughly 3000 million speakers of English as opposed to 1000 million speakers of Chinese.
This is just an assumption (and my opinion) for the future and I'm looking forward to being challenged on it
@ Bobk: I thought that the Chinese had a demographical problem as well.
I think I've heard once that they lack of enough people between 20 and 40 and thus will face a problem in a few years.
(at least they will if they keep polluting their fertile lands and rivers)