interesting concept on ZSL's behalf, and an issue which more zoos should be bringing to the fore, though im not sure ZSL has selected the right venue for this exhibit, which could probably be better interpreted using different species in another forum....such as the old aquarium for example.
to be perfectly honest, and I am a huge fan of my local fauna, it would take more than emu and wallaby to liven up the mappin terraces. If they wanted to stick to the Australian theme then swapping Red Kangaroo for red-necked wallaby would be a starting point. Adding in more waterfowl species, such as maned duck and maybe converting the old langur den into a semi-nocturnal exhibit would work.
However, climate change is such a big issue and I really dont think ZSL has even chosen the right style of exhibit to do so. Our land is one of extremes where climate change both past and present, as well as man-made influences going back tens of thousands of years have shaped and continue to shape the ecology, which tends to muddy the issue slightly and makes it harder to interpret well.
when I lived in London in 2005 there was much talk of bringing wolves and brown bears back to the terraces. This is an idea I like alot. Charismatic species. Historical ties to a heritage listed structure. A habitat which would discguise the terraces themselves. And best of all a long and interesting natural history and contentious interactions with humans on the Britsh Isles and current debates about their possible reintroduction.
ZSL would do well to even convert the old Casson into a venue for climate change with numerous sub-exhibits, or create an exhibition similar to BUGS and handpick micro-species with stories to tell, exhibit them well and link them into the issue.