I don't see it as "most powerful" (what's powerful is the American army and passport). I see it rather as most useful. It is widely-spoken and it is the language of academia and pretty much the internet.
It is simply the result of various historical events - any language could have been used. Had the Aztecs colonized the world, we'd all be speaking Nahault.
English language is powerful of course, but the most powerful one I think is Chinese. It's a language of the future.
It took centuries for English to displace French so I don't think Chinese (or rather the official Mandarin) is going to be the lingua franca anytime soon.
I don't see a shift happening, will China invade and colonize the whole world? In the past people from many countries traveled to study in Europe, often France and England. but English became widely spoken in the last century due to the expansion of the US cultural industry, this influence won't just raise with GDP. There are many factors involved, like the difficult of learning, and there's no much sense making people learn other language when you already have a huge literary archive available in English, including this post. It's most likely that in some time we will have good AI powered translators to talk to anyone in any language.