I think China already has orbiting nukes they could de-orbit if needed.
I find that implausible. It would be a breach of Article IV of the Outer Space Treaty, and one with a high risk of detection (particularly in the event of a failed launch attempt - radioactive materials are
very easy to detect and trace).
It would also be a tough engineering challenge to build a nuke that could remain in orbit for any significant length of time, and remain reliable. And any in-orbit maintenance would require highly visible and highly expensive crewed missions.
And jumping all of those hurdles only leaves you with a minuscule fractional advantage in a first-strike (and while there is a second-strike advantage, it's easier to use submarines to ensure it); If China wants to nuke someone, they can do it with ground (or submarine) launched ballistic missiles at far lower cost, and without breaking any international treaties in the build up.
There's really nothing a space based nuke can do, tactically or stategically, that a submarine based one cannot; And while it is true that in space nobody can hear you scream, it is also true that in space there is nowhere to hide.
The US (and UK, France, Russia, and probably dozens of other countries) know what satellites everyone has launched, and what orbits they are in. They don't necessarily know what each has on board, but it's highly unlikely that any have WMDs, and an absolute certainty that if a WMD were deployed by a satellite, all those nations would know right away whose it was.
At least with a submarine launched missile it would potentially be difficult for the victim to be sure exactly who had attacked them (though even there there are ways to work it out).