Looking in the games files, accidentaly I've found who's gonna be the next leaders.
In the Base/Platforms/Windows/audio/(your language) folder there's the archive Speech_Localized.xml. At the end of the text we have:
They reference the audio files inside the Speech_Localized.bnk file.
I extracted them and converted to an audible format, and I have found:
DOM_LEAD_AMA is the intro for Queen Amanitore that we already know and love.
DOM_LEAD_GIT is the intro for Gitarja, a majapahit queen. I suppose she's the indonesian leader.
DOM_LEAD_JAY is the intro for Jayavarman VII, a khemer king. So the Khmer is probably the second civ.
Thank you, oh mysterious one-post-account! ;p