Your example is bad. Fetch resolves the promise even if you get a 400 or 500 error.

If your project is going to be robust, you MUST intercept the result and check before asking for JSON.

    const resp = fetch(`https://api.weather.gov/gridpoints/TOP/31,80/forecast`)
    if (resp.ok) {
      const weather = await resp.json()
        |> x => x.properties.periods[0]
    } else {
      ...
    }

Your hack-syntax response would then become

    const resp = fetch(`https://api.weather.gov/gridpoints/TOP/31,80/forecast`)
    if (resp.ok) {
      const weather = await resp.json()
        |> %.properties.periods[0]
    } else {
      ...
    }

Hardly a big win and not at all a win when you realize that you can't copy/past code to and from that syntax without risking weird errors due to the special symbol.

`await` isn't a function and (as I noted) either wouldn't be possible or would require special syntactic consideration for F# syntax, but the hack syntax is basically one giant ball of special syntactic considerations.

I'd rather explicit async/await and keep the simplicity of the F# syntax.