Add a chat spam mode
Just like emote only mode, slow mode, or r9k mode, a mode that would allow viewers to spam as hard as they want.
Many streamers I watch (and some for whom I mod for) encourage spam when they get raided or during special moments, but because of Twitch chat restrictions, viewers can only send the same message every 30 seconds. Many viewers feel left out in these moments because they can't really spam, and the streamer usually asks for more, so everyone is frustrated in the end.
What I suggest is something like /spam and /spamoff commands for mods+ to allow viewers to spam the same messages every 5 seconds (since it's Twitch chat restriction for bots), or even for a shorter amount like mods can.
Quick note to add to the suggestion:
It came to my attention that it would probably overload Twitch servers if a lot of chats were in spam mode for a long time, and some people raised the same concern to me.
After deliberating on the subject, we thought that limiting the spam mode in duration could be a solution.
Therefore, something like /spam <amount of time> and /spamoff to cut the spam early if needed would be a solution, with the amount of time being optional and being by default and capped at 10min for example.