That would add much complexity. At least the way I picture it when reading your words (manual mark read on each message).
I see why you would want to have such a feature, though It’s rather a social issue when you get pressured by your peers to react to every message.
Adding more complexity to the UI hurts the normal user experience.
If you implement it and it makes sense UI wise, I’m happy to merge the pull request.
I’m not totally against it, It’s more like I can’t imagine how to implement this feature in a simple & practical way that won’t get into the way of the normal user experience.
Also there is a related topic about marking chats as unread to provide a reminder to look at it again, might be interesting too:
Mark Chat as Unread