Variety is the key to language change. Vocabulary is probably the most unstable. Slang, of course, is particularly fickle. Teen slang has a strong American slant, of course. For slang to be slangy it has to startle, and above all it has to be new.
Sounds are constantly on the move.
We'll probably continue to drop yods. Words such as dew, new and tune will be pronounced doo, noo and toon. We've been dropping our yods since the 17th century, but the change is so glacially slow we're hardly aware it's happening. American English has dropped most yods, British English speakers have lost least yods and, as usual, Oz English lies somewhere in the middle. Time will tell.