Comment 5 for bug 460980

It does not seem semantically correct to me that the owner be the same entity as the registrant.
What if Alice registers a series for project foo, then decides to withdraw from the project and doesn't want to be involved any longer (and that includes not receiving any mails related to activity on whatever items she registered)? Prior to withdrawing, she should be able to transfer the series' ownership to Bob, while remaining the series' registrant.