As a System Administrator, I would like availability for external LDAP authentication for emails because it would allow for single sign-on.
Having the capability of using an external LDAP authentication source for e-mails would be great. A lot of businesses use Active Directory, having to maintain two credentials set for users is a pain point. With all the hosted options available (Office365 and GSuite that support external LDAP authentication/sync), it is very easy for new small businesses to shift their focus toward these products for that particular reason.
Additionally, it would be also nice to have a built-in LDAP server, that could serve cPanel services (e-mail, FTP, etc.) and be used by external components as well. That would be a great incentive and solution for start-ups, choosing cPanel as a unified platform for their needs.