"Conversely, if there are concurrent changes to a single field, only one will be retained, which is also what we want."

They are wrong though. As HN submission illustrates, people want some order and eventual consistency, not a rule to select a single field during concurrent changes. And this is where a Lamport timestamp could help.

No matter what scheme you use, it is still a rule. Lamport timestamps, whatever are just different ways of resolving a conflict. In general, the fact that you have designed your system to have this conflict in the first place is an easier problem to solve than having users understand more complex resolution methods -- especially those that push a callback into the app design rather than actually just solving the basic problem in a pragmatic way.