@timbray I do like that idea - although I wonder if `ap://` might be be more in keeping with what users expect?

But I think the big blocker is what happens if you *don't* have an ActivityPub client installed?
I know Telegram & WhatsApp have (had?) URI schemes - https://shkspr.mobi/blog/2017/04/whatever-happened-to-uri-schemes/ - but they barely seem used any more.