[bob1029]

> an event might have changed (or be deleted) between the time it was emitted

Then I would argue it isn't a meaningful event. If some attributes of the event could become "out of date" such that the logical event risks invalidation in the future, you have probably put too much data into the event.

For example, including a user's preferences (e.g., display name) in a logon event - while convenient - means that if those preferences ever change, the event is invalid to reference for those facts. If you only include the user's id, your event should be valid forever (for most rational systems).

> your consumer has to query the service that dispatched the event

An unfortunate but necessary consequence of integrating multiple systems together. You can't take out a global database lock for every event emitted.