Dendrite is the next big thing right? Written in Rust? I'd be curious to see how the performance is there with it being in Rust and a rewrite/new implementation that can learn from experience.
I've been trying Dendrite for a few days: a single user in the system - me -, being in two, federated, medium (<1k) sized rooms on matrix.org, the memory usage runs between 250MB to 1.5GB.
I agree that Synapse, the only currently available Matrix server is resource heavy, but I would not extrapolate this to the future of Matrix servers.
There is still quite some optimization possible.