What's most incredible to me is how close tracing feels in spirit to me to event-sourcing.

Here's this log of every frame of compute going on, plus data or metadata about the frame.... but afaik we have yet to start using the same stream of computation for business processes as we do for it's excellent observability.

Any of the Clickhouse-based Otel stores can do event sourcing - just set up materialised views on the trace tables. I know the following use CH: https://uptrace.dev/ https://signoz.io/ https://github.com/hyperdxio/hyperdx