@Erhune
I like your idea. When I was developing bots for IRC, the server also had a partner developer program, which had increased limits for privmsg/notice etc.
I personally think that it would help Twitch, if developers are able to program games without any spam for twitch. Yes, the chat is mainly for communication between streamer and viewer, but there are also some bots already which have games included like a heist.
Apart from games, whispers could also be used to improve the moderation of a channel.
For example can a moderator subscribe to notifications so he will get a whisper why a user got timed out/banned in a channel and for the duration.
My bot is for example tracking the duration a user is in a channel. Here I can use whispers, so a user can ask for his total duration and the answer will also be a whisper, which would result in less messages in the chat.
In general you can use whispers to communicate with special users more directly, which will reduce the amount of messages in the normal chat.
English is not my first language. Please forgive me for mistakes.