TMI is IRC. One and the same. TMI (Twitch Messaging Interface) has a IRC compatible endpoint.
It doesn’t make sense to have followers in TMI as TMI deals with chat, the delivery of chat, and anything related to displaying chat on the Twitch website.
Personally makes more sense to put follower notifications into PubSub. But the ONLY thing that having follower notifications here is for third party, it wouldn’t be used on Twitch’s “core” product(s). That being chat and video. So don’t hold your breath.
I and everyone else don’t have a problem long polling a cached end point.
Your use case @phosphorcat is not more “real” as a reason than the existing solutions cover.
Moving (or providing) something like this to a PubSub or TMI level interface is way more “expensive”, given people like to spam follow/unfollow streams anyway [metrics needed], so getting those notifications thru the stack (reliably) is way more expensive given it has to be multi user/consumer safe across thousands of channels.
Basically, it’s not simple as you think it is, and it’s way better/safer/cheaper to deliver a the same page of data over and over again to a consumer refreshing the page than thinking about and choosing to deliver a notification over the events stack.
As to your suggestion about “quicker follower alerts”, 3 minutes which is about the “average” delay due to edge side caching is perfectly fine, for most applications, which last time I checked was what followers was trundling at.