There was a recent staff statement that, contrary to previous discussion, there will be a new architecture version of smart lighting and it will have mirror capability. So maybe this all gets resolved once the transition is complete. 
Meanwhile, as long as you have a hub, there is a community-created edge Driver specifically to enable mirroring. You might take a look at that and see if it fits your needs.
(New Release) Edge Driver Virtual Switches Mc (virtual Switch Mirror and virtual Switch Board)