This latest 'enhancement' is utter madness. It does nothing to improve the utility or user experience of the site, it's deceptive, misleading and demoralising for hosts.
When I rely on reviews to make a purchase decision I'm only interested in those which give a contemporaneous account of the quality of the offering; and this makes perfect sense. Unless I'm travelling by time machine, why would I give a flying **bleep** what the place was like 2 or 3 years ago?
In particular, the decision to order reviews so that the reader is presented first with the views of those from their own country of domicile makes a mockery of Airbnb's espoused principles of inclusiveness and the breaking down of cultural stereotypes through the mechanism of inviting 'strangers' into our homes. Your ham-fisted attempt at improving functionality is so obviously informed by your own cultural biases that it's a PR disaster in the making.
As a guest, I would find it offensive that Airbnb presumes that simply because I am located in Australia, that I would value the opinion of other Australian domiciled guests over those from other parts of the globe.
Seriously Airbnb, do you think that just because we live in a particular country we all think alike? What next? Are you going to push reviews written by female guests over 50 up my list whenever I view a listing because, of course, we all think alike?