I am not sure what the code behind the “You’ve read this post; click to bookmark it.” and “This is the last post you’ve read.” ribbons are, but what @pekka is asking for does not seem any more presumptuous than what is already in place.
The possibility of misclicks and tabs opened for later perusal did not stop those ribbons from being implemented, so those should not be grounds for not implementing the acknowledgement feature in the same way.