Channel Super Moderators
It is nearly impossible to coordinate with a large group of moderators (for big channels) on who should and should not stay banned. Typically, this is what a user blacklist would be for, but there's no good way to implement it on twitch.
It would be ideal for Super Moderators to be the only ones able to permanently ban and unban permanently banned users, while normal moderators could only timeout and untimeout.
It would also be useful for Super Moderators to be able to timeout normal moderators, or unmod them completely.
I have years of experience moderating and administrating forums/community dialogues, and I can say having tiered user roles is completely necessary for a coherent staff structure. Notice how chains of command exist in nearly every organization imaginable. That's not an accident. It's the most effective strategy.