We have dabbled with a house rule where if China controls all the Chinese territories, then Chinese forces can venture past Chinese borders. That would mean the Chinese fighter could fly out, attack Japanese ships then fly back to China. The main reason was certain games where Japan was busy at sea or something and the Chinese managed to capture all Chinese territories. This ends up with a large amount of Chinese troops staging in Manchuria yet due to the rules they can not advance into Korea. That just seems silly to me.
If you’re using this house rule, you should add one where IF China reclaims its capital, it has to build industrial complexes in order to place units normally, and loses its “build anywhere” ability. It only makes sense, if you’re going to allow them to leave China. It can keep the bonus for the road, but not build other types of units due to the Chinese Civil War. Just an idea.