Conditional PUTs aren't possible with versioned objects, but if you desire immutability, then they do help.
To implement serialisation, (as opposed to using Conditional PUTs) one could implement a ledger on top of versioned buckets with LegalHolds: Basically, the object versions part of the main chain are LegalHolded whilst other versions are reconcilled (rebased) onto main and later deleted. Tricky to implement, for sure, compared to say, maintaining a journal in DynamoDB to track PUTs to maintain serial integrity.
