3 reasons why I believe this upcoming DLC will have 3 new civs

1. It seems like this DLC is similar to DOI where Indians was split into 4 civs - 3 new and 1 reworked.

2. The 2 unofficially confirmed civs - Jurchens and Tanguts have appeared in the 3rd mission of Genghis Khan campaign. It won't make sense if they leave the main antagonist of 1st and 2nd mission - The Khitans aka Kara Khitai who are without honor.

3. Last announcement says it will be one of the most exciting DLC for AoE II DE. A regular 2 civs DLC is not gonna be one of the most exciting. It will be exciting nonetheless.

That being said, don't be surprised if the DLC cost 20 USD since the base game price is now 35 USD.