Make chat more tolerable and reduce spam by temporarily pinning cumulative messages, with the number of people saying it, in the chat.
Twitch chat in popular channels is more about reactions than it is about actual chat. Unfortunately - as fun as chat spam can be - it makes moderation difficult and completely destroys any semblance of discussion that the streamer or chatters may want to have. r9k mode was an answer but, unfortunately, breaks down the way certain chat bots work and ruins, rather than facilitates, certain forms of chat that streamers may want.
I propose that streamers be given the option to enable a customizable "popular messages" feature for their chat. Such a feature would catch any message spam and "pile it up" while, depending on popularity, pin messages with a number next to them showing how many people have reacted with that message.
As an example, let's say a streamer does something warranting a :pogchamp: message. "Person 1" types :pogchamp: and their message is shown in chat. "Person 2" types :pogchamp: and their message is shown in chat with a "2" next to it to indicate that 2 people have now said this message while "Person 1's" message is deleted. "Person 3" types :pogchamp: 5 seconds later, it gets displayed as a new message in chat with a "3" next to it and "Person 2's message" gets removed.
Essentially, the message is being "pinned" to the bottom of chat by people spamming the reaction message and the number next to it is steadily increasing, showing just how popular the streamer's actions are via how high their reaction numbers get. The name next to the chat will always be the last person who typed the reaction with the possibility of removing the name when the number breaks a customizable threshold. The streamer should be able to adjust things like how long one of these pins should go on for (eg: for 90 seconds after the initial spammed message or 30 seconds after the final spammed message) and APIs should be able to take advantage of this so streamers can feature popular messages on their overlay. The streamer should be able to customize how many pinned messages can occur at once so the chat doesn't just fill up with spammed-over-time messages.
Finally I think it would be nice if the numbered indicator grew, changed color, animated, or allowed customization based on the relative number of chatters spamming the same message. This could encourage chatters to participate in the spammed reaction-fest and create a greater sense of unity among communities.
Also customizable: The option to pin spammed messages at the top of chat rather than at the bottom.