The problem with all the other solutions is that they end up being language-specific. That article you've linked to lists the various languages that chose that route: Go, Lua, Ruby. Now try invoking a Lua coroutine from Go, and have it interop properly with goroutines while running.

The nice thing about async/await is that it's just a wrapper around futures, which are themselves a composable wrapper around callbacks (semantically; the implementation can be more efficient, of course). So any language that can express function callbacks as first-class values can represent a future, and any language that can represent a future can interop with the async/await world. Which is why you can have JS code doing await on C# code doing await on C++ code in a Win10 UWP application, and it all works. And you can take existing libraries and frameworks that use explicit callbacks (often written in C), and wrap that into futures such that it's all usable with await.