Two corrections: 1) We are not using Go in all of our servers. Java, C++, and Python are very prominent. Go is just getting started internally. 2) Dart is being used internally, we won't be dropping it.
Can you say which internal projects are using Dart at Google? Were they new systems, rewrites, or evolutions of existing JS systems?
They got some patches from the finance department and Google were really insistent on adding big integers to JS so it looks like they're using it for currency. Woo... exciting.
Dart is an unilateral project aiming to: "ultimate goal is to replace JavaScript", "rescue browsers from JavaScript" or "Google preps Dart to challenge JavaScript". Being open source here, is not good enough.