Online we tend to read these conversations as they’re being written, as people are engaging in live conversations.
I think that Online we tend to read these conversations as they WERE written. Starting at the top. Wading through the middle. Skipping to the end.
If we were joining a conversation, we would join at the (current) end, then try to figure back to get some context, then join with a comment relevent to the (current) state of the conversation.
Which is to say, conversations should be “top posted”. Which might excite an avalanche of criticism, but would be an interesting excercise.