I looked at the exchange in the GitHub issue page and it seems to me that the real underlying issue is that only your primary Gravatar is allowed to have a display name, bio, etc. I guess there is a reason for that, however what I expected was that each email/gravatar could have its own details to display in the hovercard.
I don’t see a reason to have one as primary, but that may be just me and I wouldn’t mind the option to set an email/gravatar as default, or even being forced to have one, as long as I could control what details are displayed for each email/gravatar.