Russia wouldn't know what to do with them, given that they effectively do not develop weapon systems after the collapse of the Soviet Union. China probably has decent enough espionage they don't really need them, although it might make a nice political overture.
And to clarify, this was a bit of a tongue in cheek comment implying that the US will become friendly enough with the two big autocracies of the world so they will officially buy arms from US defense companies (in which case Denmark can pass those F-35s to them).
For the record, I dearly hope it doesn't come to this, but right now I'm not sure.
