very cool, but one problem is: as social media posts virally spread by people re-posting them, you are supposed to get mostly replies from people that you don't know at all - that's where the wisdom of the crowd comes in that makes social media so powerful. if you only get replies from people that you follow - most of them likely don't even follow you back - you basically just have a group chat with your closest friends, a small echo chamber.
True, we need ways to extend beyond the bubble. I think we might be able to store 3rd degree contacts even on mobile browser clients. Native clients or at least relays can store up to 4th degree, which I believe covers most people on the internet. Also one simple thing that can help is showing posts from unknown users that your social graph reacted to. Completely unconnected users are tricky, I can't see a spam-proof way to accept messages from them besides zaps.