I haven’t really read the entire thread, but I know the feeling. I use forums primarily for feedback and criticism, and I’d prefer not replying to x topics with the same canned “I read your post but have to think on it before acting” response. Maybe a plugin would be better suited to this?
The behavior could be as simple as @mentioning a person, and if that person viewed the post, a checkmark appears or some sort of acknowledgement of having been read appears.
If the idea is a general “users have read” acknowledgement, then thread view count does a lot to convey this already - but it should probably differentiate between “logged in” and guests who aren’t likely to reply.