This would be nice for our organization as well.

Currently, we have servers in various enclaves (dev, test, staging, production, etc.) and we test upgrading to newer versions in the dev and test environments.  After testing the new version, we currently then have to revert/roll-back to a database backup to return to running on the older version.  It would be nice if we can test out the new version, and then just go back to running the old version without having to do a full database restore.

Jira has a startup parameter, -Djira.downgrade.allowed=true which allows an older version of Jira to start up and operate using a database that has already been upgraded to a newer version.  This means it isn't necessary to keep backing up and restoring the entire database, we can just toggle between Jira versions and keep using the same database.  I realize there is a risk that there will be application problems in this configuration, so it's obviously not intended to be used in production, but it's very useful to have a Jira server in our dev/test environment that I can quickly toggle between any version of Jira that I want without needing to constantly restore database backups.

I agree,

Bitbucket would be ideal to downgrade;
Company COMP has a server ABCD with BBv1 installed on it.
Now BBv2 comes out, and it cannot be run on ABCD, and requires BCDE.
Later on, COMP reduces its capabilities and must revert to server ABCD. They can no longer use BBv2, and because their data cannot be reverted they also cannot use any of their data.

Hi klfoong

Thanks for the suggestion. Can you please expand on this request and let us know how this would be used by you and how will it help you?