Fair, though in practice they would join in anyway - China would be going for them next. Better to fight with the US than alone.

Presumably the US would find itself in such a situation because it tried to stop the invasion of Taiwan. China will never have the interest or capabilities of going after Europe.

Interesting. Edge case: if French Guyana (off the north side of South America but considered part of France and the European Union) is the victim of an attack by some means, are NATO members obliged to act in its defense?

No. The same is true of New Caledonia (most of overseas France, actually).

Nor the Falkland Islands, which is probably a more likely (although still unlikely) trouble spot.