All that there is to use, which is what almost all ‘points’ systems use, is the undocumented chatters endpoint: http://tmi.twitch.tv/group/user/CHANNEL_NAME/chatters
It’s not without issues though, the endpoint has issues more frequently that official endpoints, and most importantly it’s a list of people connected to chat, it’ll include bots, and users who aren’t even watching the stream, and will also miss anyone who’s watching from an embed or has chat disabled. It’s the best we got though and for some use cases has sufficient accuracy.
The new roadmap mentions Chatters, so hopefully we will be getting a documented and more reliable (and hopefully more data returned) endpoint in the future, but it will still likely just be a list of those in chat and still not count for viewers.
Many of us have brought up a VHS endpoint that’s for a channel rather than a game, which with appropriate scopes could be huge, but sadly no mention of if anything like that is on the table.