A passing thought while I'm in Western Australia...
WA was never part of New South Wales, so 26 January 1788 - Sydney's foundation day - can have no meaning for it per se.
The only significance 26 January can have for this part of Australia is a celebration of the arrival of white settlers on the continent. So nothing to do with the modern nation state of Australia, and everything to do with white supremacy.
It really won't do as the date for a unifying national day.
