China/Mongolia: Double up with Kublai Khan. I know Mongolia was in an XP. They’d have to find a way around it, because this one is too tempting to ignore. Xanadu as his ability, maybes gives culture bonuses for improving conquered land or building certain districts in conquered cities.
I don't think the Chinese (who have, in the modern day and age, huge cache in the computer game market by having so many gamers in their borders) would like that, anymore than the French or Polish would like "doubling up" with Germany under Hitler, or the Greeks with Italy under Mussolini.
Egypt: Hatshepsut is less likely because they’ll want to differentiate from Cleopatra. Khufu or Ramses II are likely as builders. Akhenaten would be a fun, but quirky dark horse..
Why should Hatsheput require special differentiation from Cleopatra. The two women were as different as day and night. And, at least Hatsheput WAS ethnically Egyptian and fluently spoke the Egyptian language.
Germany: Probably not Frederick the Great, since we already have a Frederick in the game. Bismarck has a history in the franchise, but I’m expecting someone who could double up with another civ, whether Charles V, Maria Theresa, or Charlemagne..
European monarchial names are so commonly re-used, even among "great monarch" that the idea "there is already a <Blank> in the game" is going to cause trouble at some point as it is. Best not to start such a precedent in the first place.
Persia/Ottomans: Not likely IMHO since they’re from DLC/XPs. I might actually expect a second leader for Arabia, maybe Harun al-Rashid, to move that capital out of Cairo..
It would have been nice if he was the leader in the first place for Arabia, and NOT one who was not an Arab, not a Caliph, and had no recognized power or lineage in Islamic jurisprudence. Don't get me wrong - I have great respect Saladin. It's just the civilization he led was woefully inappropriate to his historical situation.
Rome: We have someone in armor, let’s get someone in a toga. Cicero for the republic? I’d say Scipio, but that’s just more armor. Livia could represent the machinations of a power behind the throne. Nero as a big personality villain? There’s always the same old Caesars too. Maybe Constantine for a very different Rome? Some people expect Theodora or another Byzantine but I still think they may get their own Civ.
I think Vespasian is often overlooked.
Russia: No commies. Ivan the Terrible could be a wild unpredictable character. Would love a streltsy UU. Catherine has been in every game since Civ2. We already have a Catherine in France though, but we don’t have an English Elizabeth. Empress Elizabeth would act similar to Catherine the Great, if somewhat less obliging..
You just dismiss "commies" off hand, but how many other leaders of Russia have been less brutal, autocratic, harsh, intolerant, nasty, atrocious, and even willing to set up secret police and jail, execute, exile, or sentence to hard labour those who disagreed with them. I can't think of any, myself, except maybe Yeltsin on a good day. Also, the CPSU regime industrialized and modernized Russia, and built it into one of the two most powerful nations in the world during the Cold War, and won their greatest struggle for mere survival - "The Great Patriotic War," or the Eastern Front of the European Theatre of WW2. No Tsar came remotely close these global and transformative achievement, and since morality and respect for human rights isn't a comparative issue either way, I wouldn't dismiss the "commies" so simply, I'm afraid.