Google would need to do this internally. Good luck convincing the 10,000 developers inside of Google stop using Java. Sure, they aren't all on Android, and there are plenty of people using Go, or Dart, or Python, but moving a company culture that large away from Java doesn't happen overnight.

Obj-C to Swift won't happen overnight at Apple either, but it is much more likely to happen because they've been gradually working towards it for years now with LLVM and such.

Indeed. Developers look to Google to set an example, but it seems that Google itself is looking to developers to set an example. Hence we have a circular pattern of language adoption :) But it doesn't have to be that way.