Give channels the ability to ban all recently created accounts from chatting in their channel
This is similar to the idea of banning abusive troll users at a certain IP address, https://twitch.uservoice.com/forums/310201-chat-messaging/suggestions/7956255-ip-ban-from-channel.
In that request, a Twitch dev gave the following reasons for why such a ban would be hard to implement:
IPs change. A lot. A broadcaster might lose a significant portion of their audience, and viewers might get confused if there are a lot of banned IPs (such as universities).
System load. Looking up a enormous list of IPs to see who is allowed to watch on every single video play is an enormous system load I’m not sure we’re willing to take on.
Support costs. “Why can’t I watch X/Y/Z, I don’t know who they are” would come up. Our support isn’t free, and we’d like to be able to focus on issues like passwords, bugs, etc.
I propose something slightly different to get around the problem of IP addresses being an unreliable way to ban toxic, abusive troll users. Rather than ban an IP address from chatting, give individual channels the ability to block *all** "recently" created accounts from chatting in their channel*.
So, for example, give individual channel owners the option of blocking all new accounts created in the last 24 hours from chatting in their channel. After 24 hours, the new accounts are then allowed to chat.
Such a feature would make it harder for persistent trolls to evade chat bans by creating new accounts. It also doesn't depend on a user's IP address, it is address independent.
I mean, some broadcasters, like TotalBiscuit, don't even allow anyone who's not subscribed to chat in their channel, by making chat subscriber only. A temporary chat ban of recently created accounts is like that.
This would make it so that a recently chat-banned troll can't just make a new account and immediately return to trolling a particular channel.

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Kozaka commented
"If you have 10 troll accounts that are 6 months old, then just ban 10 troll accounts. Done, won't have to be bothered by the same troll until X days/weeks/months later."
This could be in normal case not the situation be! If one streamer reports those 10 troll accounts with a log, etc., Twitch should ban that accounts in 1 sec with one click.
However, Twitch does not care of their streamer Affiliates, and do not ban anybody. So...this solution can help a bit, for really new troll accounts, but not for old ones.
I reported many of troll users, and none of them were banned in the last 4 years. Thank you for your support Twitch!
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James commented
If you have 10 troll accounts that are 6 months old, then just ban 10 troll accounts. Done, won't have to be bothered by the same troll until X days/weeks/months later.
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James commented
If this gets implemented, it would also be really helpful to streamers if statistics were provided on what their typical random viewer looks like. Like demographic data, but instead of being about human age, gender, etc, it would be about what the distribution of **account** ages are, and what the distribution of ages are for accounts that end of getting chat-banned.
Providing that "demographic" data would allow streamers to make more informed decisions about how old a new account has to be before it's allowed to chat in the streamer's channel.
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James commented
If you want to give broadcasters even more fine-grained control, also give them the option of specifying how old an account has to be before being allowed to chat, like 1 week, 2 weeks, etc.