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I know you didn't ask for this sort of answer, but you could use user profiles for this.

You can have more users on the "standard" AOSP Android as well, but with a certain AOSP-derived you can also have notifications forwarding.

Until they add Application List Scopes (I believe it's on the road map), in the exactly the same way users can now lie to apps they have only specific contacts in their contact list and only one or two specific folders in the Storage.