Chat loves custom alerts! Right now, custom alerts for donations are limited to the amount of the donation (exactly/more than a certain amount). However, a great thing for chat interactivity would be the ability to trigger custom alerts based on chat input on certain events - specifically, bit donations and subscriptions:
EXAMPLE 1: A viewer donates bits and inputs the text #lurker as part of their message. This triggers a specific "lurker gif" alert that triggers on stream - perhaps a clip from a stealth game, someone lurking in the shadows.
EXAMPLE 2: A viewer subscribes and inputs the text #spooky as part of sharing their subscription. This chat input triggers a special alert with a loud jumpscare noise in the streamer's ear.
I personally would like to see this ability available for donations and subscriptions. Currently, this could be done using a bot command, but making custom alerts unlimited would just lead to alert spam, and channel currency is not enough of a barrier to entry, in my opinion.
Both of the above examples would lead to clippable moments and drive viewer engagement, encouraging community members to want to donate/subscribe more. And these are just a few examples - alerts such as these could be tailored specifically to the game, the streamer's preference or Twitch community events/holidays, the only limit is the imagination of you and your community!