Why was Elemental Chat chosen as a proof of concept? What is this proving?

Elemental Chat was built as the simplest test application for the Holo platform and testing Holochain at scale. It is not a production ready application.

We chose chat because we knew that it would put Holochain and the Holo hosting infrastructure to the test, challenging their ability to power high-throughput, low-latency apps — the kind of apps people use every day. If any app could expose bugs and performance bottlenecks, this would be it. The success we have seen has enabled us to move forward with developing the primary Holo apps (Host Console, Publisher Portal, and HoloFuel), with enough experience to feel confident that we can continue improving and deliver great user experiences.