What I am not following here is why make people click “I read it” when we already know they read it.
We track read state on all posts.
I can see some value in adding publicity visible read state on private messages, especially when groups are involved. That is where experimentation should start.
Additionally this solves the problem described here without littering public posts with messy metadata. You send a PM to staff when you make an announcement, and can tell when they all read it.