China itself suggested that others could be allowed to make use of the facilities the new islands provides.
However, that was before all the bad blood with the FON patrols, so whether China still feel so generous is very much up for debate.
I think even if China was to offer to open up their bases for use by others, who gets to be on the invite list would very much depend on their attitude and behaviour thus far.
Had Australia asked before mounting FON patrols themselves, China might have indeed indicated that they would be welcome to make use of the facilities. But I think the Australians are being very optimistic if they think China will still be willing to roll out the welcoming matt now that they have effectively taken sides against China.
Although there is still a chance that China will forgive them their transgressions, since it has done in a relatively low-key fashion, and limited in scope. Especially as doing so would neatly undermine a lot of the opposition to China's island building, and also potentially drive a wedge between the Australians and Americans.
The USN would firmly be on the "not welcome" list irrespective of what China agree with the Australians in my view.
I agree this is the best course of action.
But I think that an invitation for the USA to utilise the new SCS islands should be held open - on the condition that they agree to certain terms set by China