ldelagoutte jeffshurtliff Akenefick I heard back from Engineering. This is indeed a gap in the API. The issue has come up in the past, yet a formal ticket for a feature request never came as a result.
I think the best path moving forward is to file a ticket through Support. Bugs/Enhancements/Feature requests have more sway when they come from customers than only from within. Be sure to mention the both the inability to get subscribers to a label as well as the need to interact with subscriptions not limited to the user account making the request.