Almost all of features revolving around the Chinese menu in the upcoming expansion for Crusader Kings 2, Jade Dragon, has some precedent in history, but like everything else in CK2, the historical value of these events are dialed up to 11.

Some mechanics have zero historical precedent. For example the idea that you could request a Chinese princess under a Chinese prestige system where you accrue "grace" by sending eunuchs you send to the emperor has zero historical basis. The practice of receiving humans as tribute has no precedent in Chinese history until the Yuan dynasty. It's possible that it was even introduced by the Mongols.

Requesting princesses seems to be based on the Tang era situation where China was facing many threats on several fronts, especially the Tibetans and nomads. In this instance the Tang absolutely did "give out" princesses, however there are several qualifiers. They were only married out very reluctantly, and always under military threat. Also, most of them were of dubious lineage and only distantly related to the imperial clan. In effect, imperial marriages were a tool of political expedience, carried out under threat by external powers. There are zero historical instances outside of the Tang dynasty when an imperial princess of one of the mainstream Chinese dynasties was married out to a foreign power. Not even during the Song dynasty did the Song dole out princesses like CK2 would have you believe. In total maybe a dozen (probably less) "real" imperial princesses descended from the royal lineage were married out throughout the united imperial era. They were all during the Tang dynasty.

Similarly the "request a Chinese expert" has some basis in that Chinese were sometimes acknowledged as having technical knowledge in some areas such as siege works, paper, printing, gunpowder, and porcelain production. After the battle of Talas, an Arab historian recorded that some Chinese were captured during the battle and Samarkand had the benefit of high quality paper ever since. This is where the idea of paper spreading to places outside of China starting from the Battle of Talas came from. However, this even is completely outside the timeline of CK2, occurring several decades prior to the earliest bookmark, 769. Moreover, archaeological evidence proves that paper had spread to the middle east at least several decades if not centuries prior the Battle of Talas. And again, these "Chinese experts" were always captured. Nobody ever went to China to meet with the emperor and request Chinese experts. They simply captured them, which to be fair to Paradox, is simulated in Jade Dragon by the raiding system.

There is one instance where the Korean kingdom of Goguryeo sent envoys to China to request certain materials related to technical knowledge. For example the print version of the Buddhist canon, which they would later copy and reiterate upon using their own set of print blocks.

The gist of it is yes, there were Chinese "experts" utilized by Mongols, maybe in Korea, and certainly Chinese culture had a very large impact on the Western Liao dynasty, also known as the Qara Khitai who invaded the Seljuks in the middle east. But the way in which these are gamified and turned into mechanics as they work in Jade Dragon never existed. The Chinese powers, whether they were Tang, Song, or Ming never gave out their technicians working in paper, printing, gunpowder, and porcelain willy nilly. There's a reason why it took Europeans so long to figure out how to make porcelain. It's not like they could just go to China and import a bunch of Chinese porcelain workers and ship them off and show them how it works. There's logistics, a huge language gap, differnt working conditions, smuggling, different materials, everything involved would have had to work right for the transfer of specific technologies.

I'll do a breakdown of Jade Dragon's features and there historical basis:

1. Request invasion. This is probably based on the Qara Khitan invasion of the Karakhanids and the destruction of the Seljuk dynasty. There is some evidence according to Biran that the Karluks initially invited the Qara Khitan to invade their Karakhanid overlords. The Qara Khitai, also known as the Western Liao, was a sinicized Mongol people led by a distant member of the defunct Liao dynasty. They defeated the Seljuks at the Battle of Qatwan in 1121 I believe, which led to rise of the Khwarzmian dynasty and the fall of Seljuk Iran. The closest a mainstream Chinese dynasty got to invading the middle east was probably Gao Xianzhi who reportedly reached as far west as the Caspian Sea. Tang influence was checked by the Abbasids at the Battle of Talas and Chinese influence in the middle east did not rise again until the Mongol Empire when they brought Chinese troops with them during their invasion.

2. Fireworks guilds were mentioned at one point or another. Gunpowder was invented in China around the time of the start of the Viking age. So around the time of the 867 bookmark. However it was not used for warfare until the 10th century. They were used as incendiaries and then an assortment of explosive and propulsive weapons during the 12th to 13th centuries of the song dynasty. Theyre typically categorized into four main categories, fire arrows, bombs, fire lances, and hand cannons. However there is no evidence of any fireworks guilds being set up by Chinese outside of China. Evidence of gunpowder appeared in both the middle east and Europe around the mid 13th century. The probability that they learned of gunpowder through Chinese influence is high however. Middle eastern sources call saltpeter Chinese snow or salt from Chinese marshes, fireworks as chinese flowers, rockets as chinese arrows. The earliest European gunpowder formulas contain the same defects as chinese gunpowder such as the inclusion of Sal amoniac and arsenic, which don't do anything. Cannons appeared in Europe during the 1320s, a few decades after China. There is one piece of evidence that cannons appeared as early as the 12th century in the western Xia dynasty, but this is disputed by some historians. Cannons appeared in the middle east by the 1360s but were probably in Muslim Spain by the 1330s.

3. Raiding China gets you lots of goodies. This historically accurate.

4. Forcing China to open up is an anachronistic feature that probably has more to do with orientalist western views of Qing and Ming China than anything historically related to the silk road. Essentially Paradox is viewing the silk road through modern European lens. Chinese dynasties did not derive their wealth from international trade regardless of what historians of globalization will tell you, nor did they have any reason or powder to cut off the silk road so to speak. The only time that China could be construed as isolationalist during the CK2 timeline was the beginning of the Ming dynasty and after Yongle's reign. Chinese international policy during the ck2 era was essentially how do I survive and how do I deal with these nomads. The silk road trade was primarily a small volume high value trade of luxury goods carried out by decentralized local actors. On the other hand:

5. Instability in China absolutely did affect the Eurasian trade system. According to Abu zayd al Hassan, the entire silk trade in the middle east basically came to a halt after the Huang Chao rebellion in late Tang China, specifically because the rebels burnt the mulberry trees used to feed Silkworms. Despite the spread of serigriculture outside of China they were guarded closely and did not produce silk in the same volume as China. Byzantium in particular monopolized silk production and restricted export of silk, so many Europeans and the middle east still had to buy silk from merchants who ultimately got it from China or India.

6. Invasion of China is probably the most gamiest of the JD features. You can't invade China when it's unstable. You can only enthrone a relative but not yourself. This is a limitation of the game engine, programming, and the lack of China in the game than anything else.

7. China being able to invade the Bengal and Ceylon region and India as a whole. The Ming treasure fleet was able to project military power all the way to Sri Lanka and capture their king in the early 15th century. They also visited Bengal at one point, if I remember correctly during the seventh voyage. So it definitely is possible, but it would be a naval invasion rather than overland. Also I would restrict invasions of India to during golden ages. There was one instance during the Tang when a Chinese ambassador was able to project power through Tibet into India. Apparently one of the local kings treated him badly. Tibet was a friend of the tang at this point, so he went back to Tibet gathered troops invaded the area below nepal. The invasion was a success and the king was captured and taken back to Chang'an.

8. Rebel generals forming their own Chinese empires in other lands. The only example I can think of off the top my head is Zheng Chenggong, also known as Koxinga, a pirate turned Ming general. He fled to Taiwan after the fall of Ming and set up his own Tongning Kingdom, it was conquered by the Qing after his death.

9. Sinicized Altaic tribes are probably based on the Qara Khitai.

10. Displaced rebel princes. When Yongle defeated his nephew and took the Ming throne, the body was never found. There's a theory that he fled overseas and that's why Yongle commissioned the treasure voyages, to find and capture the previous emperor.

Also, from my understanding, they will begin the game with the Tang Empire

As a slight clarification the initial Dynasty depends on which start date you choose. The Tang dynasty are only for the earliest two starts in 769 and 867. Outside these two specific scenarios you can choose any date between 1066 and 1337 and the initial dynasty will be either Song or Yuan depending on date.