Ability to react to individual comments with emotes/emojis (a la Discord)
On Discord, you can react to a message with an emote or emoji. This allows people to react to a comment without clogging up the chat with "LOL" or "yes/no", etc. The streamer would be able to opt-in to it to prevent it when it isn't wanted.

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SurrealJC commented
Yes, keep it simple though like just the basics:
Laugh,appreciate,depreciate,roll eyes/groan, mad, maybe a COUPLE others
As for the design I imagine 2 concepts: first is the classic/obvious emojis appear with a number next to them.
try to keep the options to ~6 reactions.
Also maybe cap the reactions to 10 so in bigger chats its less likely to cause attention anxietyBut a better option might be to have it be an animated bump on your comment. Someone clicks the comment,selects one of two reactions: positive or negative and then the author (or everyone) sees the comment bounce/shake/flash/confetti or shadowblink/*****&crumble/submerge/explode.
The biggest issue with this I can imagine is a LOT of new chat clutter, and its a huge waste of energy/bandwidth (remember every bit of data costs energy to send and receive).
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MugSkillet commented
for a previous chat txt, it would be great to have just an emoji response w/txt like slack. Some times people chat some funny things would be great to do a lol, heart, or some other emotes. I am sure Twitch has an emoji dept.
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ReDe_ commented
THIS! Why i need to reply with "LUL/Kappa/etc." or just spam emotes when i could just hit the emote directly for the comment