I can confirm that it works in getting userslist now in Chatzilla by going to Preferences -> irc.twitch.tv -> Lists -> Auto-perform and adding the /raw CAP REQ :twitch.tv/membership and /raw CAP REQ :twitch.tv/commands
Also got it working in Hexchat.
Edit: this is before joining any channels which works for me since I manually do /join #channelname anyways.