What about metadata protection? Whenever I hear people talk about how unsupportive Signal / Moxie is of federation and how federation would be better for everyone's privacy, my question is this: In case of Signal you only need to trust one provider (Signal) with your metadata (who's talking to whom) whereas with a federated network you have to trust your provider and all providers your friends use.
On top of that Signal has a track record of standing in for their users' privacy[0]. That probably can't be said about the administrator of some random Matrix server.
[0]: https://signal.org/bigbrother/eastern-virginia-grand-jury/
