Within 10 years, American English will be incomprehensible to the modern speaker. Not only will it be flooded with new words, borrowed from immigrant communities and online speech, but the American accent will suddenly and dramatically shift. This will be in part from a new generation, determined to distinguish itself from previous generations, who they will hold in contempt.
But some of it will come from the rise of a new international accent, adopted by young people everywhere and spread through the internet, that draws inspiration from a yet-to-be released Japanese cartoon set in an optimistic future, for which the filmmakers invented a new, futuristic accent. It will be the first example in history of an entire international generation simply choosing to have a new accent, although regional variations will quickly develop.
Nonetheless, it will render the next generation largely unintelligible to their elders, which will be its purpose.