That said, the timeline and quick switching ideas are very cool. So many chat apps implement a text search and stop there, this is a clever way to find a specific point in time, or find specific non-text content.
But given a hint about their level of presence, what are you doing with that information? What can you do after sending the message you were already going to send? Worst case it makes people send "???" as a follow up because they can see I'm coherent enough to tap a notification and assume that means I'm available for a full conversation. The opposite example is the typing indicator, which acts as a useful mechanism to keep a conversation ordered and flowing once it's started. Maybe an argument could be made for the "currently viewing" indicator being more useful, since it solves the problem of indicating I'm available for a conversation better than just "read y/n".
2. Before read receipts, I used to get very anxious about whether I was being ignored, now I can see that the other person simply hasn’t seen the message. Was that a personal problem? Yes, and frankly it probably would be significantly less of an issue now that I’m older.