For a real-time discussion I think new posts have to appear at the top.
So an upside down topic.
If you have an all day chat with over 1000 messages (like the OP) anyone joining has a lot of reading and scrolling to do or hit the bottom button.
Join right in with the ongoing conversation at the top.
Make an upside down topic work and put one one in everyone’s user profile page and call it say a “wall”? 
The emoji is joy …I thought it was crying buckets when I chose it …