I know this is a late reply, but here's a suggestion for Chinese UU: Lisheng ("sages of rites" 禮生/礼生 lǐshēng), a Confucian missionary that gains X gold when spreading in foreign cities, maybe depending on the city population/culture/commerce, or calculated exactly the same as city conquest.
I think it is more suitable than fire lance for several reasons:
(1) Chu-ko-nu is good enough a counter to melee and light cavalries, and fire lance seems to be redundant.
(2) Chinese game plays barely involve massive land conflicts except versus Mongolians, whose light cavalries could be countered by Chu-ko-nu already. Even if other land conflicts were expected, Chinese are usually favored due to a technology edge. So a land military unit might not be necessary at all.
(3) Historically Chinese dynasties have been diplomatically active since BCE (Han dynasty), which is underrepresented in the game where all Chinese UHVs are internal. A missionary UU to foreign countries is a way to emphasize this missing aspect.
(4) The gained money reflects Chinese tributary/cefong system. Another historical flavor.
(5) It synergizes well with the Confucian URV.
(6) Game-play-wise, it provides Chinese a better economic recovery from early-mid game settling.
(7) I am not a modder, but my guess is adding this function to the unit is not too much from combining 'spread a religion' (missionary units) and 'conduct a trade mission' (GM units).