Alright, I've looked into it. There are 27 people in the CHA.OS general chat. Anyone who doesn't have GCAT somewhere in their username aren't going to be important.

The Full release kids are AG, GG, and TG.

Ly'lac is GC. Ly'lac's friend who has dialog is TC. Ly'lac's other friend is AA. AT is currently banning everyone. CC and CT are listed in the CHA.OS member list.

GA, GT, CG, CA, AC, TA, and TT have yet to be mentioned, but at least one of them is going to be Yiffy.

Theory time. The missing links share usernames with Kanaya, John/Jake, Karkat, Eridan, Nepeta, Sollux, and Dirk/Rose. Yiffy will most likely be GT, since Rose is TT and Jade is GG. Four humans. 6 Dirk/Rose creations. 6 empty slots. They could be more Rose/Dirk creations. They could be members of the returning cast. Non-canon Nepeta and ghost Eridan. I can't imagine any other feasible options.