This was an interesting little bit of history I wasn't aware of. Australia trying to use its unique wildlife as a diplomatic tool makes some sense... There are lots of species that only live on the continent due to it long geological history of isolation. However, none of the species I can think of quite match the panda in its blend of public appeal and difficulty to care for and proliferate. It's not like there is some global collaboration of zookeepers trying to figure out how to get koalas or kangaroos to reproduce. If anything, koalas might reproduce too much.
I also read through the first piece on China's panda diplomacy as well. I was already somewhat familiar with the story of how the Nixons were able to normalize relations with China partly through the exchange of pandas. Smithsonian has a piece on it. I wasn't aware of how much the diplomatic exchanges with Japan mirrored those of the US at essentially the same time. It does make sense though since post-war Japan has had their foreign policy so closely aligned with that of the US in the Pacific.