If Russia tried to conquer Xinjiang, I'm pretty sure they'd ask China for help.
The Russians made steady encroachments on Zunghar territory throughout the early 18th century (Omsk was built to expand Russian power in the Zungharian steppe, for example), though it was helped by the presence of the Qing tying up the Zunghars' hands. Without a strong China, there's really nothing stopping the Zunghars--and possibly the Khalka as well--ending up like the Kazakhs.
Even if a merchant-warlord like Koxinga doesn't take power, the trends of the 17th century will encourage a mercantile, maritime focus
Just as the trends of the Song-Yuan period encouraged a mercantile, maritime focus?
Any native Chinese dynasty in the 17th century will come from the Northwest macroregion, which is both close to Beijing and a place where the hand of the gentry and the state is very loose. There's simply no other region that can compete; the Yangzi or North China macroregions have no real reason to leave the Ming regime (and indeed, these places didn't revolt OTL) while the southern macroregions like the Southeast Coast and Liangguang are too faraway from places that matter. Plus, without 18th-century population movements in these areas, their potential to shake up the Chinese state is much lesser than, say, during the Taiping.
You can see this is the case because the principal "peasant rebels" during the late Ming crisis originated in this single area.
The Northwest region also happens to be the most insulated from both commercial and maritime changes. It wasn't properly integrated into the Chinese national economy until the 18th century, when the Qing made a drive to develop the region because it was so critical to the war effort against the Zunghars.
the institutional nature of the Qing state inhibiting it.
I don't see what this nature is, because the Qing were the single regime most open to maritime trade since the 14th century. Kangxi allowed all maritime trade in 134 Chinese ports and Chinese people were free to leave their country again (there were some restrictions, but nothing serious and a lot of these were intended for popular welfare, e.g. the prohibitions on rice exports). This sort of liberality compares favorably to Song or Yuan openness.
The Qing were so liberal that 18th-century Southeast Asia essentially became an economic colony of China, with its largest city (Ayutthaya, then Bangkok) becoming majority Chinese, its market economy in Chinese hands (especially in Java), and even Dutch colonies, where the VOC tried to direct all trade to the colonial capital of Batavia, trading more with Xiamen than Batavia. This simply cannot have happened if the Qing had a strict policy against maritime trade.
I certainly think proto-democratic ideas were flourishing at the time.
Democracy is a concept in Western political philosophy that rises from the specific circumstances of European statebuilding, where different social classes were in conflict. It isn't something that really works in the Chinese context, where the state was "fractal"--its actual authority was very loose, but the local gentry's desires for a Confucian society generally aligned with that of the state (hence why the Qing could get anything to work while one magistrate was in charge of 300,000 people). See R. Bin Wong's
China Transformed: Historical Change and the Limits of European Experience. People like Huang Zongxi and Gu Yanwu were anti-imperial autocracy, not democrats in any sense of the term. And given that both scholars were ultimately statecraft scholars and wrote as a response to the Ming-Qing transition, I find the simplest hypothesis the most likely; they wrote in response to the political failure of Ming autocracy. Like, that's what they literally say; the collapse was caused by the autocracy of emperors in a Mencian sense, and that is why autocracy was bad (this traditional basis of 17th-century philosophy is evident when you see Gu praising literal
feudalism). The Qing restored confidence in the imperial system.
When that confidence faltered and crisis continued, you see late Ming patterns repeating; the
jingshi scholars, people like Hong Liangji and Wei Yuan, the rise of literati cliques like the Spring Purification Circle.
The reason the Qing had to rely on the Jesuits in the first place is because they had an institutionally inward orientation.
See above. "Institutionally inward" is a pretty big claim to make when the Qing understood Inner Eurasia by far the best out of all Chinese dynasties since the Tang (save the Yuan), when they essentially abolished the tributary trade system, and when they fully freed up maritime trade for the first time in centuries, possibly for the first time in Chinese history. The Song only had ten custom houses, while the Qing prior to the Canton System, as I mentioned above, had 134: 24 in southern Jiangsu; 7 "major" ones and 11 "small stations" in Zhejiang, plus fifteen "branch stations"; 20 in Fujian; 72 in Guangdong. See
The Qing Opening to the Ocean: Chinese Maritime Policies, 1684-1757.
A focus on "practical learning " was a constant refrain among Late Ming reformers-not so much in the Qing period.
....Are you serious? Have you really never heard of Qing Evidential Learning and Statecraft scholarship? Practical Learning was huge under the Qing. When people like Chen Hongmou--one of Qianlong's most trusted officials--go around saying that imperial examinations should only measure the Practical Learning of the candidate and founding Confucian schools in backwater provinces and explicitly ordering them that the only curriculum offered should be Practical Learning, I simply cannot take you seriously.
See William T. Rowe's
Saving the World: Chen Hongmou and Elite Consciousness in Eighteenth-Century China.