The current metadata leaks in Matrix are due to an architecture that makes every participants’ homeserver store events that reveal chat participants.

If you are concerned about metadata, run your own server, p2p won't help you here because simply put: you still need a hosted highly available homeserver, otherwise the UX and reliability will be unacceptable to most people. Anyways, this is overstated and exaggerated a lot, people leak metadata to their ISP and their favorite cafe's wifi router all the time. If anything that can be done it will be added to Matrix, in the meantime, it is the best there is.