So, it makes sense if you have infinite testing budgets.

Personally, I prefer exhaustively testing the upgrade path, and investing in reducing the time it takes to push out a hot fix. Chicken bits are also good.

I haven’t heard of any real world situations where supporting downgrades of persistent formats led to best of class product stability.

Would love to hear of an example.

They might be an appropriate safeguard for a prototyping shop, but not for Delta.