Enforced Mesage Ordering

[nambrot]

Current Behavior:

Message senders currently do not get any ordering guarantees from the protocol.

Related issue: #5352

Expected Behavior:

Message senders can get ordering guarantees from the protocol.

Open thoughts

Would an ordering hook and ism work? I.e. you allow message senders to specify an ordering hook (maybe with a nonce/salt in the hook metadata). The ordering hook would send a message to the ordering ISM with a commitment to the original message ID and nonce. The ordering ISM can then be enforcing explicit ordering of the messages. Nice thing here is that senders have the ability to opt-in. They also can have different ordering per application logic.