What geographies are they sending these invites to? From Reddit, it sounds like northwestern states of the United States (people in Washington and Idaho have got them).

I wonder if anyone from Australia has got an invite? I get the impression that the answer is no.

It makes sense to me why in early phases they'd restrict it to the US – putting aside geographical issues around where their satellites and ground stations are, restricting it to the US means they only have to deal with one regulator, the FCC; every additional country is another regulator to deal with, and different sets of rules around matters such as privacy, lawful interception, metadata retention, etc.