With UUIDs there is absolutely no need for that.
> Keeping an actual transaction open for that long is asking for contention
Yes, which is why this is not an actual db transaction, it's a business transaction as mentioned.
> and the idea of having data hanging around ephemerally
The data is not ephemeral of course. But also the mapping between business transaction and model is not 1:1, so while there is some use for the transaction ID, it can't be used to identify a particular model.