It would be a terribly complicated change, even more complicated than last time I looked at this.
The problem is that we have lots of code that keeps “unread counts” on topics list right even if whispers are around. So there are a bunch of columns that track “what staff can see - count” vs what “non staff can see - count”.
At a minimum we would have to rename all that stuff but then there would be even more changes to permission model and so on. It is quite a huge change probably 2 weeks of work to get it working right with no performance impact beyond what we have today.