One more thought - any consideration of hooking this to Cloudflare's queue? Then you could optionally connect another worker to that and e.g. persist everything in their D1 SQLite database.
I haven’t looked at the queue specifically, but Durable Objects have a nice key/value storage mechanism that happens to map nicely. It would take a bit of munging to make it work for a stream instead of a single value, but I have a design in mind.