Part of me says some sort of meta tag in the page header might be better, defining what sort of activity this is, and then users install browser extensions made by the fediverse apps they use to interact with them. That way if a non-fediverse user clicks the link, they can still access whatever it is. But a fediverse user would get a prompt like "Open this (thread/user/hashtag) on your own instance so you can interact with it?" Or they could set the extension to just do that automaticly for them.