Although I have not used it as DO, I have been using it for durable workflows for a few years. The cached results of the workflow activities could give the feeling but the latency to read and write would be a dealbreaker for many. There is a lot of overhead in writing the interface between application code and Temporal workflow (for example, you can have conflicting object IDs that can be configured).

Self hosting Temporal with a Postgres datastore is usually how I deploy it and it works great, but at that point I'd just write it to a Valkey store if I just wanted a easy DO interface.