Bridging P2P and Normal Matrix without creating point of failure

**Link to problem area**: https://arewep2pyet.com/

**Issue**
According to Are we p2p yet, it is intended for P2P Matrix to be bridged to the main protocol through
> A server which can bridge traffic between P2P and normal matrix e.g @ed25519-key:server-name.com or a bridge.

I wonder what’s the current thinking on implementing this bridging server. My concern is it could potentially create a point of failure like `matrix.org` which can get blocked in hostile nation-states (China, Iran, etc.), thus wiping out the very benefit of using P2P in those situations.

Start with the issue description and the linked Are we p2p yet? problem area; no source file, test, or entry point is named. Investigate the current Matrix P2P-to-normal-Matrix bridging design and document a direction that avoids a single point of failure, with the relevant specification changes identified as the definition of done.

Written by the indexing model from the issue text.