As the title suggests the emperor of china should be allowed to take male concubines. During the Han Dynasty It was actually very common for the emperor to take a male concubine or a "favorite Male" and this wasn't a euphemism for a different court position that was just lumped in as a concubine they were a male lover for the emperor who would be part of their harem and serve just as any other of his wives/concubines. Though this position was a dangerous one as now you were part of the emperors household and therefor under the same threat of assassination or other political intrigue (such as being falsely accused of impregnating one of the emperors female concubines as the male concubine was the only non eunuch allowed to see them other than the emperor himself) it was also a position in which one could further their families position in the empire. After all, if you become the emperor's favorite boy toy, maybe he'll give your family members a few positions in government. The only argument I can hear about the "historical accuracy" of allowing this is that the Han Dynasty is not in power during the time of CK3's start dates as the Han Dynasty rained from 206 BCE to 220 CE. Though in a game ware you can have a Muslim HRE, a Norse japan (I'm looking at you Koifish), or even have a Fr*nch character who lack the traits Lustful, Gluttonous, and Ugly should it really out of the question to allow a Gay or Bisexual Chinese emperor to reinstate male concubinage? I can see the next question, "why from a game-play standpoint would this be useful?". Well I can think of a few reasons why having the option to take male concubines would effect game-play.
By taking a male concubine you stop that male from marrying another character. This could be strategically used to insure that a specific families perfect heir can't have any children to continue the family lineage.
House relations with the Emperor could be improved from a positive relationship with a concubine, therefor sending your gay, beautiful son with high diplomacy to be the Emperor's boy-toy can help the rest of your family move up.
New events revolving around male concubinage.
And I'm certain some of you reading this can come up with more ideas. What you you all think?