Ability for moderators to mark a chat message as interesting for the broadcaster to view.
In rooms with a lot of viewers things can be very crowded, making it difficult for the broadcaster to read and respond to chat.
One method for dealing with this is to allow channel moderators to tag interesting chat messages so that the broadcaster can see them easier. These messages could be highlighted to the broadcaster, made persistent like a "sticky", or even a filter mode so only tagged messages will show.
This offloads the work of finding significant messages within chat to the moderators instead of the broadcaster who's already preoccupied with the game.
This relies on the broadcaster choosing moderators ahead of time who have good judgement on what messages should be tagged.