This almost feels like it should be a trait that a workflow can set at a top level, as a config checkbox similar to realtime processing.

I dont think it makes sense in the context of a step, because those are independent of the workflow, and are tied completely to the event. This is more about the order that the events are queued and executed by the workflow manager.

If this was done at a step, then it would need to look at all other instances of a workflow and block if any others have a timestamp earlier and then we can just say please wait and try again later.

Being devils advocate, I think this could be done at the step level which would allow all the steps before it to be done in any order and then it would throttle them to be in order and then potentially any steps after this could run out of order again. Not sure if thats a feature or not.