And I thought we would only get one new faction in 2.4 along with some other features. This is absolutely wonderful news, I am eagerly anticipating 2.4 now.
The previewed units, like all BC units, are amazing. One of the things I love the most is the variation among soldiers.
I guess the new factions will be: the Imamate of Yemen (obviously), the Atabegs of Mosul, the Kara Khitan Khanate, the Principality of Vladimir-Suzdal and maybe the Kingdom of Ethiopia. This is in line with my hope that the new map will already be included in BC 2.4.