[5Qn8mNbc2FNCiVV]

This seems blown out of proportion. Anyone who knows how streaming in React works knows, that you can't stream your HTML line by line. And there was the need to not block first paint (HTML, not JS) just because of metadata. It's reasonable to have a list of user agents that are exempt from that behavior since those are also not the bulk of your traffic where you want to show something as fast as possible.

How would you instead solve this, with the requirement that some users have metadata that takes a while to load?