I agree this is a very good idea and it would save users a lot of time. In my experience with other CRMs, including those I’ve built myself, this feature was a ‘given’. The (temporary) duplicate email issue can easily be resolved by appending “clone_” to the original email address in the cloned entry form so (1) it is unique, and (2) its bogus so it won’t work until the local-part of the email address is changed, while keeping the domain part of the email address intact.