I don't know about long gone. I still support a websocket solution that needs to have server-push as a fallback because of browser incompatibility issues.

It shouldn't be a problem for about a decade [0]?

What's your hit rate for the fallback?

[0] https://developer.mozilla.org/en-US/docs/Web/API/WebSocket

The hit rate for fallback is pretty low. It was less than 5% the last I checked.

This 5% includes or excludes non-human traffic?

Includes.

Do you have some specific examples?

Old Android handsets seem to be the big ones.