Just in case Purism monitors this thread I will also +1 for Australian concerns about the modems.
Taking the information from the modem frequencies section of the FAQ (puri.sm/faq/) and local carrier information from frequencycheck.com, it looks like the PLS8-E modem will work in Australia but have no coverage in the USA (assuming I am interpreting the documents correctly) and vice versa for the PLS8-US.
I do a reasonable amount of travel, sometimes to the USA, and even though the modems are swappable I don’t really like the idea of having to look after a spare modem while I travel and swapping a modem on my knee in an airport shuttle.
The lack of one modem with some chance of working in Australia, Europe, and the USA is a major disincentive for me.