After upgrades, sometimes you find certain plugins don't work or some subtle piece of functionality is failing and maybe you don't notice for a few days. After even one day of Customer Support we might have 500 new issues in Jira. This makes rolling back to the old database backup a bad idea.

It would be nice if there were some sort of tool to take an exported XML file and downgrade it to a previous version that could be re-imported.

Certainly not a trivial thing but it would be cool to have such a thing!