The client-server model has been the given way to implement communication between two peers for a long time now. Part of why is that it's hard to establish a connection to an arbitrary IP endpoint over the internet. Various peer-to-peer networks have tried, and some of them succeeded, over the years using intermediate globally reachable rendezvous points. The problem though is that of interception.
A general rendezvous point over IP is able to surveil and intercept the traffic between the peers. The level of surveillance and interference depend on the protocols being used but at the minimum, metadata is accessible to the intermediate. We have a privacy problem.
Tor onion services provide self-authenticating addresses and end-to-end connectivity over the internet. If you know stuff about the internet, this sounds like magic. But NAT punching, strongly authenticated communication is a thing and onion services deliver it. Building services on top of onion services is the future for privacy preserving communication. If this sounds interesting, take a look at Briar. They're ahead of the curve and serious about privacy.
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