We use Discourse to offer technical support to our customers. And we miss the “read ack” button too.
Of course for us the “like” semantic is very different from the “read” one. The usefulness of the “I read it” button is to show the original poster that I’ve read it, without polluting the thread with acknowledge messages, as stated above.
You (@codinghorror and @sam) keep saying Discourse already knows of the read state. But how a user can know of it? I don’t see it anywhere on the GUI. The proposed feature here is about an easy information on who has read the message (in the same manner the like info is currently managed).