You are trivializing a migration that involves more than ten times as many components. Here's my todo list for the same problem:

- gmail - drive storage - calendar - contacts - keep - photos - music - domains - Pay - adsense - webmaster tools - analytics - authenticator - Home - maps - chrome - youtube - Play - email at external sites

Can you explain your idea about using Cloud Identity Free Edition in order to allow an email at a third party to own Play Store apps?