Backseaters and Spoilers in Chat
Right now there is a constant conflict between people in chat "backseating," and people in chat who don't want spoilers.
I have an idea that I think could greatly reduce the severity of this conflict.
If Twitch were to allow phone-number-verified accounts to flag another user as "backseater," and if streamers could only allow users into chat if they are below a certain "backseater count" (flagged as a "backseater" by ten users or less, for example--ideally a threshold the streamer could change for each stream), streamers would finally be able to enjoy doing a first playthrough of a game with minimum backseating and spoilers.
It wouldn't solve the problem of unwanted backseaters and spoilers in Twitch chat, but it would greatly reduce how rampant they currently are.