Will this satisfy GDPR requirements fully? What if that key had somehow been involved in an unknown leak in the past (of just the keys) and then the data is exposed somehow in the future?
Leaks are punished, as they probably should be, under gdpr anyways. But now do we have to account for all of the keys over time and have it be probably gone? What if we take backups of the systems that stores the keys? Do we have to purge those backups as part of the deletion request? What if they're terabytes in size?