I'm not against the idea of full CRUD in the UI (it would be nice), it's just that it'd take more work than I think it would be worth.  Either you have to store subscriptions in two places, or you have to have a weird encoding of system_ids in SNS, and I'm not even sure if that's possible.  The payoff doesn't seem worth it, unless there's legitimate demand for it.

You're welcome to investigate it.