Richard has a very popular public image, but while he may have been an excellent Crusader he wasn't much of a king. He spent about six months of his reign in England. For a religious England, I'd recommend Edward the Confessor.
good leader who isn't one of the traditional picks, Ulysses S Grant
You proposed
a leader, but where's the
good leader?
Grant's administration was heinously corrupt--not because the president himself was corrupt but because he was a very poor judge of character and a rather uninspired administrator. For that matter, he was competent but not exactly brilliant as a general.
Emperor Meiji has a lot of potential in my opinion.
Not if you want the game sold in Japan, where depicting an emperor is taboo. Which is a shame, because I agree that something different would be a nice change. Ongoing shogunate Japan it will have to be--and kudos to Firaxis for at least breaking from the Sengoku period with Kamakura-era Hojo Tokimune. I propose a Heian leader next time...if for no other reason than Heian Japan was obsessed with aesthetics, which means Japan's leader will be very flashy.
Sun Yat Sen is a good nominee as well. I am woefully ignorant of Chinese history, so I know only a few dynasty names, let alone their rulers, but I have no doubt that there are other great candidates amongst the Ming, Qing, Song, and other. China should have like four or five different leaders realistically, but certainly having only one is a tragedy.
The weakness of the Chinese Republic is what led to the civil war between the Chinese Nationalists under Chiang Kai Shek and the Communists under Mao, resulting in a situation where no matter who won, the people of China lost. There are plenty of great emperors of China without resorting to the more controversial leaders who have presided over China since the fall of the Qing. (NB, Firaxis, that Qin by no means needs to be a staple, nor does Wu Zetian--though of the two I prefer Wu. How about Taizong of Tang or Wu of Han or the Kangxi Emperor, as awkward as that is to say in English?)
one of the four Rashidun caliphs
If I'm not mistaken this violates the Islamic prohibition of not depicting religious figures--but I could well be mistaken.
both Arabia and Al-Andalus
Considering that what Civ calls "Arabia" is essentially a blob of all the Islamic Caliphates, al-Andalus is, strictly speaking, part of Arabia--though as Civ moves away from blob civs, I would welcome a Caliphate of Córdoba civ under Abd ar-Rahman III.
I'd love to see her back...in Civ7. In Civ6, I'm not sure what she brings to the table that Peter doesn't cover. They come from the same era, and broadly speaking they have a similar legacy of Westernizing Russia.
We should probably bring back Napoleon, no question.
I mean, he has name recognition, but he's so
boring. I mean, you object to Catherine the Great reappearing, but Napoleon has been in every Civ except II and III. Louis XIV is equally famous--or if we must have a Napoleon, Louis Napoleon turned Paris from a backwards Medieval firetrap into the city of avenues it is today. (We just won't talk about his foreign policy--NB Bismarck was equally a failure at home as Louis Napoleon was abroad. I've often joked they would have made a great team with Louis Napoleon running domestic affairs and Bismarck seeing to foreign affairs.
)