I have been exploring workflow orchestration for sometime now - specifically Temporal. Temporal's authors don't recommend it for very high throughput (per workflow) use cases, although I haven't benchmarked it myself. Also using it in a SaaS environment, I would prefer some serverless deployment strategy which possibly allows scaling down to zero.

I have my eyes on flink stateful functions http://statefun.io/ The abstractions are quite low level as compared to Temporal but the overall ability to write tasks/activities as serverless functions which have access to state is quite attractive.

Would be happy to talk to someone who has explored this further.