Spec got merged: https://html.spec.whatwg.org/multipage/links.html#link-type-modulepreload
I think <link rel="modulepreload"> is currently one of the most important features to be implemented in WebKit, as pages load a lot slower without this.
Note that modulepreload should also be supported in link headers.
(In reply to Noam Rosenthal from comment #4)
> Note that modulepreload should also be supported in link headers.
Indeed it should! But modulepreload is probably a lot less commonly used in link headers, so it isn't really of very high priority.
Is the WebKit team interested in implementing this? As already mentioned, this would significantly improve page loading speeds in WebKit, which I guess should be very important to Apple if they want to increase Safari's market share. Because why would anyone want to use Safari if they know that sites load faster in Chrome because WebKit doesn't support an important web standard?