You can implement synchronization across DOs, but the application has to coordinate it. E.g. you could implement two-phase commit to get strongly consistent sem

You can implement synchronization across DOs, but the application has to coordinate it. E.g. you could implement two-phase commit to get strongly consistent semantics (with the possibility of temporary unavailability if the network between the objects is partitioned at the wrong moment). Or if your application can tolerate eventual consistency, consider using CRDTs for partition tolerance. These things require some care to get right, but not a huge amount of actual work, compared to the challenge of implementing lower-level consensus and replication that DO takes care of for you.