My two cents

[Kagamin]

On Tuesday, 24 October 2017 at 07:29:08 UTC, Satoshi wrote:
> If we want to use D for GUI development we will need this 
> feature anyway.

To not block UI you need non-blocking IO, and async/await is not 
required for it: vibe provides non-blocking IO with synchronous 
interface. And here we also have another shortcoming of 
async/await: it doesn't interact well with GUI that traditionally 
uses synchronous event handlers (mostly because it predates 
async/await).