Is this still set in stone though? Especially as an individual DLC, Tibet should be possible to add with some courage. It would be such a worthwhile addition!
Tibet has been playable in EU4 and CK2 for years, and they are sold in China as well. Tibet even has a mission in EU4 called "End the Chinese Threat," which needs them to go even farther into China than the historical Empire did and take over the mandate of heaven. If that's no problem for the censorship...
Paradox games are sold in China on the grey market. They aren't actually marketed there and they aren't approved by the government to be sold there. So says Johan, who decided that it wasn't worth the hassle after previous dealings with the Chinese government. I guess this might have changed in the last year or so, but probably not.
Suffice it to say that treating Tibet as anything other than part of China now and always is definitely a huge red flag when trying to get a game approved for legitimate sale in China.
We'll probably go too far off topic if we continue, though.