Yesterday at Kamailio World there was an interesting question, raising a concern about replication of user location and DMQ in general, we should track it in the mailing list and use it as a feature request and I can share my initial thoughts on the topic.

The concern was about DMQ reordering transactions.

With SIP registration this seems like a minor concern, high responsiveness at the cost of potential small inconsistency seems like a good option.
Considering that, the state will automatically correct itself and that this can be controlled using the expiration timer.  This will become even more insignificant when the replicas can only be used as primary server failover. (it becomes a very small concern only when the primary server fails)

With other type of data re-ordering may result in more problematic use cases.
My impression is that DMQ should try to be good only with volatile data, data that will expire anyway, like caching with expiration, registration, Dialogs, etc.

I think it may be worth looking at adding support for ordering/queuing in DMQ.

Performance and simplicity could be maintained by doing mainly transactions in parallel with a configurable re-ordering best effort to minimize the impact of the problem.

For example :
1- trying to re-order for a configurable amount of time. (32 seconds to match the RFC for SIP re-transmissions)
2- adding tractability for failed transactions.
3- the possibility to trigger a re-sync.

Another option is to look at preserving strict ordering but I can imagine this could add more problems in some cases ...