Prediction: In 2020, networked communications have leveled the world into one big political, social, and economic space in which people everywhere can meet and have verbal and visual exchanges regularly, face-to-face, over the internet. English will be so indispensable in communicating that it displaces some languages.
An extended collection hundreds of written answers to this question can be found at:
http://www.elon.edu/e-web/predictions/expertsurveys/2006survey/englishtoplanguage.xhtml