I suspect the difficulty is that right now fibery doesn’t even track “open” rate of anything. So it can not know what was read and what was not.
And it’s quite complex to implement I think since it’s hard to know what counts as “read”.
Is it if the entity is opened? What if the comment field isn’t showing? What if it’s showing a different entity view? What if this entity view has so many fields and the comments are all the way at the bottom?
It could be implemented as “comment rendered on screen”, (not sure how feasible that actually is though) but it’s something that doesn’t exist at all yet, and would only work for the comment primitive, which I’m not personally the biggest fan of, but I think might happen according to this: