According to http://www.ecma-international.org/ecma-262/6.0/#sec-future-reserved-words
"await is only treated as a FutureReservedWord when Module is the goal symbol of the syntactic grammar."

This code should be illegal I think:
http://www.typescriptlang.org/play/#src=import%20'foo'%3B%0A%0Alet%20await%20%3D%203%3B

Came up when discussing TS semantics with @ajklein (v8 ES6 module expert).