Relays should also index each other, users and notes on a DHT like s/Kad for discoverability. Relay could be a simple desktop app that anyone can run then. 

 the DHT might be the bridge, but ideally mobile first 

 Mobile is a challenge for anything but client because it's ephemeral and changes address very frequently.  

 i was wondering if my above post was going to make it out to ther clients... it appears yes