"Under attack mode" to get rid of all bots.

Twitch should introduce an "under attack mode" similar to the one in Cloudflare that many sites use. If you are exposed to an attack by bots, you switch on the attack mode and everyone who then tries to reach the site must first solve a captcha (in twitch cases, everyone who wants to write in the chat). Then all bots will be filtered out.
When the attack is gone, which is usually 20min-30min, this mode is turned off and everything is as usual again.

This is better than having your stream ruined with spam.