Where did I say this? In any case, yes, we are moving to parsing emoticons on the server because the number of emoticons is growing too quickly. Requiring clients to be aware of all emoticons is a burden on clients, especially given that a very small subset of emoticons are used in a typical user’s session.
The format is mostly defined internally at Twitch, but is subject to change, so we will not publish it yet. I will add that both the emoticon parsing and the IRCv3 changes are being QA’d as I type this. You can expect a release in the next 2 weeks.