Yeah it’d be terrible until P2P Matrix is done https://arewep2pyet.com/
Discussion
Almost all of the metadata leak is in the centralized identity server, I am proposing using no identity server at all and relying on public keys ans local contact lists.
Also, there is no alternative, Signal is not an open protocol or a federated network that you can integrate in Nostr clients, it is either Matrix or reinvent your own.
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.
All the chat participants should also have their own homeservers, which would be P2P.
Regarding UX, I believe onion-routed store-and-forward is in the works.
I am all for client side embedded servers/nodes, but you didn't solve much if you still need a store and forward server.
The only difference here is then, users will be custodial of the signing keys instead of the server offering availability. Is that a good thing? Depends, it comes with its pains.
Regardless, metada will still leak, that's the nature of relaying data in a performant way, as in non-onion-routing
IM metadata hasn’t been leaked to network operators ever since the wide adoption of HTTPS.
Sir routers can see what IPs you are visiting, regardless of Https, so unless you are using Tor you are leaking metadata, even a VPN is just changing who you are leaking to.
If you make VoIP chat using webrtc you are leaking your IP to your contact, even in Signal, hell, you are leaking your IP to signal server all the time, it is all tradeoffs.
There is no such thing as perfect privacy.