Well, yeah, that's how it works now.
I'm looking at an improvement to the current system. Admin views can change, and in this scenario they're a form of centralized power and responsibility. Delegating this particular power and responsibility to the user would remove the additional burden of moderation and allow the admins to focus on running the instance rather than policing the Fediverse.
Giving users the choice of where their content is federated seems like a happy medium for all parties concerned. The admins don't have to get political and the users can stay away from the Zuckening if they want to.