One feature I've thought of would be for someone in a conversation thread to know if the other participant upvoted their last comment. Giving someone an upvote and not replying would send a strong positive signal without taking up more space.
Here's an exchange from a book I thought of while typing this comment, to illustrate my meaning.
`But he could not resist the temptation to speak and to awaken a little human warmth around him. “A pity for the car,” he said. “Foreign cars cost quite a bit of gold, and after half a year on our roads they are finished.” “There you are quite right. Our roads are very backward,” said the old official. By his tone Rubashov realized that he had understood his helplessness. He felt like a dog to whom one had just thrown a bone; he decided not to speak again.`
I think I dislike it because it reminds me of the busy exec replying with a single word, and that is definitely lacking in humanity.