I'm mad the browser has gotten not at all better at doing HTTP. It's criminal that Fetch never developed Push support[1], and now the browser is removing it, having never let us even try to use this capability. I think things like multi-way streaming are probably much more doable with modern Fetch, but I'm not totally sure.
The browser folks have such a narrowminded view on what http is for. If it can't help them load pages off one of their CDNs faster, they don't care.
[1] https://github.com/whatwg/fetch/issues/65