I should not need an Identity record for a Trivial Identity

(Bug, Closed -> Fixed, Priority: High, Test Status: No automated tests yet , Reported By Justin du Coeur, )
Internals, Invites
Summary: Currently, we have to have a DB record for all Identities, even the completely empty ones created from Shared Links. That's adding bulk to the MySQL table for no good reason.
How hard would it be to make this optional? There is no good reason for this MySQL row, except that the code expects to find it. Since the IdentityId is all that is "real" in this case, we shouldn't need a row for it.
The complication would come if this Identity becomes real later. We would need to detect that situation, and add the row when needed. That seems doable, but a bit delicate.