The Sultans Ascend could be cool thematical expansion, but I guess, that developers do not want use AoE4 potential for some hidden reason.
Instead of Joan of Arc, Order of Dragon or “Zhu Xi’s Legacy” (BTW, what it is?), there could be the Templars, the Hospitallers, and Teutonic Knights as variant civs, or 2 crusader variant civs + Ayyubids & one more variant civs for Ottomans / Abbasid - for example Seljuk Empire , as mentioned by @Veridamar
the crusader units are already in the game due to in-game picture from DLC steam page
Joan of Arc “civ” looks interesting, the Order of Dragon and “Zhu Xi’s Legacy” were not revelead yet, but what do have these “civs” do with crusades and sultans?
I am glad that Byzantines and Japanese are finnaly comming to AoE4, but these civs are very interesting (that is, why they are demanded by players), Both have potential to have own campaign expansion in the future