What about is_domain_in_list() that is allowed to receive an email address? If @ exists, we explode on it, otherwise, we just assume the whole string is the email.
I like that idea. See 15706.4.patch, where I also pare down some of the new testcases that shouldn't have been there.
As for the function names, I agree that they're not good. is_email_address_unsafe() is, as you note, highly misleading, but it seemed beyond the scope of this ticket to change something that's already working as intended. The newly proposed is_email_address_allowed() just parallels the naming convention, which comes from the name of the saved site option. I also agree that the UX is not great, though I don't have any bright ideas about how to make it much better.
In any case, I hope that the peripheral crumminess of existing UX and function names, etc, doesn't get in the way of getting the current enhancement - wildcard domains in the white/blacklists - into 3.7. It seems to me that the UX stuff could be handled in another go-round, independent of the specific fix being considered in this ticket.
http://core.trac.wordpress.org/attachment/ticket/15706/15706.4.patch
