It’s a good idea, but fedi is maybe too broad to be useful? I wouldn’t want a Lemmy post to open in Mastodon, and pretty sure opening a Mastodon post in Lemmy is impossible unless the post was directed to a community.

web+threadiverse could solve that issue but that’s kinda hacky. Maybe the real solution is to improve Lemmy and Mastodon so that they are capable of doing these things decently.

I was actually thinking of making a browser extension that handles this instead. Each Fediverse software could write something to window.fediverse or something like that, with tags for group support or micro blogging. The extension could have methods to infer these values for existing platforms. But the extension could give a dialog box to redirect, based on your preferred instances for certain tags.