Most of those characters are based on real life people, and thus, are ineligible.
Man do I have news for you about Dr. Kawashima.
I still don't believe this to be the case, and I don't think Sakurai would reject putting a Warriors character in Smash solely because they existed in real life. KT's version of the characters are distinct enough to be more of a video game character than their real life counterparts.
Real people are kinda tricky to include. Even if I think I've been here before (DW made me reconsider my opinion a bit from when I last disscussed this topic. More on that later)...
Oh yeah. Dr. Kawashima licensed and signed his name and likeness for Nintendo to use. Also, the Brain Age games (and his AT / Spirit) do not allude to Kawashima's real work as a neuroscientist. That's a bit easier. Historical figures on the other hand...
Nintendo can't exactly contact said historical figures and ask "Eh, uhm, excuse me Mr. General (referring to Zhao Yun), we come from hundreds / thousands of years (Zhao Yun died in the year 229) into the future. Excuse us, but could we get your likeness into a, ehm, this fighting game which runs on not animals, nor water power, but on
controlled lightning?"
Pre-1800s peoples' minds officially blown.
I mean, there's one Spirit that's important in this discussion: Allessandro Inzaghi, from the GBA game Napoleon (a Fire Emblem-esque game released in Japan and France.) Inzaghi, for the record, never existed, and he's the only Spirit from that game in Ultimate. No Napoleon, no one of his generals or friends (not even Jean Baptiste Bernadotte, who later became King of Sweden under the name Charles XIV John. The current Swedish king is a descendant of Bernadotte) not his enemies. Because including Napoleon or any other historical character would raise a couple really uncomfortable questions. Such as:
"Does this Spirit battle rep this historical person?"
Now that's a massive can of worms. Even on people who have generally-agreed upon legacies, because suddenly the general public will notice "Oh, Napoleon's in the same game as Super Mario!" and there would be heated discussions around that. Professional historians would have to weigh in. Nintendo might want to avoid that most of the time.
That said, I kinda think DW has a bit easier route - Kid Icarus' spirits include real Greek gods, sure, but it's Kid Icarus' (different) take on them, not really based on the Greek myths. DW could go a similar route, going for example "Lu Bu (Dynasty Warriors)". And Dynasty Warriors seems to be pretty popular in China, which eases things further. Also, DW is based on the
Romance of the Three Kingdoms, a very important cornerstone of Chinese literature (written during the 14th century). Not
Records of the Three Kingdoms, the historical document written around the 3rd Century (
Romance was based on
Records. With its own twists.).
I don't think a DW rep would be immune to the heated debates listed above, but I can see them having an easier time. DW's characters are twice fictionalized from the real people. Or a fictionalization-on-a-fictionalization.