In the future will you be able to be the Emperor of China with its government while following the native Chinese Folk Religion? (forgot the name the mod uses; I think it's called Shennist?) I found it kind of weird that you couldn't, but that was in September so it could have changed. I'm somewhat against the religion restriction, as I think that practically you only have Taoism or Shennism to pick from when owning the Chinese heartland (unless you like no moral authority and exploding into heresy if you pick anything that can have heresies), but if the restriction were to stay, I think that the Chinese Folk religion should also be a religion you can follow while maintaining the Empire of China government system.
Speaking of religion, is it possible to do anything as a Nestorian in China or is it just there for historical purposes?
I've been considering revisiting that restriction at some point (it isn't a priority at present), but there are some potential issues with allowing it for other religions. One issue is that we'd allow people to play as a Chinese Imperial China without JD (or RoI, since that also allows playable Taoists), though since it would be perfectly possible to mod in a government with the exact same features without JD that isn't necessarily a problem (especially since our Chinese Imperial already isn't 100 % the same as the vanilla one). Another issue is that access to the Grace system currently is tied to holding China and being Chinese Imperial (and having JD active) and that that system might become nonsensical with a weird HF Shenist reformation (e.g. if you go Warmongering/Unrelenting + Enatic Clans + Daring + Temporal, your China suddenly is very un-Chinese, and even with fewer changes you might have a rather weird China), though implementing a stricter trigger there might work (though certain parts of the Grace system might need to be disabled for a reformation that might allow most of it; if you pick Polygamy, the general system might still be sensible, but sending concubines to China is no longer an option, and if you pick Divine Blood then Imperial Marriages shouldn't be a thing since the EoC should want to keep things in the family).
There's also the fact that we have to determine what we consider "Chinese enough" and that we'll probably not satisfy everyone
regardless of where we draw the line, and it would risk becoming a mess to implement less strict requirements. For example, someone might argue that a Han Reformed Muist (with Cosmopolitan + Meritocracy (or the unique Muist doctrine, which grants the benefits of Meritocracy) + Stability + Autonomous, which essentially is the same as what Taoism has (it lacks Hermetic access (which hardly is overly Chinese) and a couple of other minor things)) ruler of China is "Chinese enough" to get access to Chinese Imperial (and being the "target" of the Grace system, with JD). Perhaps that character might be (and perhaps we should consider allowing that combination, if we are loosening the restrictions), but what if the culture (or even base reformed religion) was Norse? What if one (or more) of the features was swapped out (and what if the swap was X to Y, rather than X to Z, or A to B?)? What of other near-Taoist religions (e.g. Buddhism and Jainism shares a bunch of features with Taoism, as does our Shinto religion)? What if the character belongs to the (newly added; there's a small reveal that isn't just a map tweak!) Bloodline of a Chinese Imperial ruler (pretender or not)? What if their
dynasty is from the Chinese culture group (possibly even a historical imperial dynasty), even if the character isn't? Even worse, for those who might
not particularly want to play a Chinese Imperial China (for whatever reason) but want to play as China it might not be particularly welcome if we are very generous with what we allow, unless we also add a way to turn it off (which would be extra work, regardless of how it was implemented).
I'm not going to say that a change
will happen, or that a change
won't happen, but it isn't a decision I'll make lightly (or that I think that someone else should make lightly; it isn't strictly my call to make, even if I implemented the current restriction with full permission at the time), and
if the decision is made to allow a Chinese Imperial China for more religions (with or without access to the Grace system, in whole or in part) it wouldn't be as simple as changing one line of code, even before we consider stuff like weird reformations and whether there are combinations of culture/religion/Bloodlines/dynasty/etc. that should be exceptions to the normal rules (whether allowing or disallowing things).
As for Nestorians in China, I believe that we only have (or
had; the current internal 3.0 version hasn't got China in it yet due to the map update not having gotten that far, and character/title history hasn't been transferred at all at this point) provinces rather than characters at present (at least inside China proper; there were some Nestorian nomads to the north, I believe), suggesting they only were there for historical purposes, but they were there since before I joined the team so I don't know if there were any plans to do anything with them or not, and at present adding anything special for them isn't a priority (updating our files for 3.0, adding some
small things that are "necessary" to add for 3.0 (e.g. unique Doctrines for our pagans), the map update, and filling in title histories at least at the top liege level are the main things we're focusing on right now). You'd presumably be able to play a Nestorian in China without any actual issues, though, since your liege(s) won't have religious title revokation allowed unless they change to a non-Taoist religion (or culture-swap from the Chinese group, since that removes the (feudal, Tianxia) Confucian Bureaucracy government at present).