I spent a little time thinking about this concept and how it relates to just having dummy account you control, for giving to services you don't fully trust.

As long as you use a secure password, and you don't use the same one. I don't see alot of difference, but the ability to sandbox each service to a list of email accounts, so that the attacker never knows the master account, would be an extra layer of security.

Utility exists here. I just don't think there's enough utility to justify the work.