I think it's fair to assume no collaborative text editing would actually occur on that field at all. And so last write wins is perfectly acceptable strategy her

I think it's fair to assume no collaborative text editing would actually occur on that field at all. And so last write wins is perfectly acceptable strategy here and no coordination is actually necessary, and neither is necessary to inform the user about conflicting edits. For UX it might be useful to observe own edit, but that can be done completely locally with data only eventually propagating farther. Incidentally this is also pretty much the only way to make the edit reliably synchronized with the remote system, because users don't have perfectly reliable computers, perfectly reliable internet connections and won't wait long for anything.