Yes, discord as an example would be awesome, exactly what I thought.

Is this back of envelope pricing include the traffic/bandwidth of the readers?

That could easily be 10-100x of number of messages.

This solution together with a cheap/free caching layer (especially for non members/writers) could be amazing.

BTW, a classic example would be an hn mirror. ;)

Yeah, much of the base cost I mentioned was from the compute, networking and S3 write costs, which could sustain a lot more messages for sure. It also depends on the number of active streams/rooms, the throughput bursts, as opposed to a steady state.

But as we speak, I am in the process of running open-benchmarks on AWS with cost attribution. I'll be posting them in the docs with transparency soon enough.

Read and write through cache already exists today, which would work in favour of both cost, latency, and consumer reads fanout.

I like the HN Mirror over a Discord-like app for simplicity. No doubt that's where my weekend is going!