Another crazy idea of mine: Would it be possible to create a smaller Australian desert exhibit with free-flying birds (finches/softbills OR psittacines) and lizards? I was thinking Pogona sp., Tiliqua sp. or Varanus exanthematicus. Would this be possible, and if yes, which lizard/s and bird/s would you use? I'm looking forward to hear your responses!
Zebra finch / Long-tailed finch & Pogona (vitticeps) could work, if heating/uv light systems are adequately and safely adjusted. Care should be undertaken to prevent the lizards from larger amounts of avian feces (i.e. careful positioning of nesting/sleeping options). I'd not recommend keeping a Varanus species together with finches or parrots, except in combinations where the bird isn't considered a worthwhile prey for the lizard (like adult Komodo dragons and Java/Timor sparrows).
Perentie monitor would relax on branches. Gazing would be sort of their hobby. Green junglefowl would cluck while Fly river turtle swim in a cooled river as Australia is very hot. Zebra finches and Gouldian finches will sing, thereof entertaining visitors in the walkthrough exhibit. In the branches above you, Emerald doves, Laughing doves, Squatter pigeons, Diamond doves and Peaceful dove will rest staring at visitors who looks like predators to them and their chicks. On your right, Blue penguins will swim in the warm water, sometimes pecking at Hawksbill sea turtle due to their curiosity. In the shallow parts of the pool area, you'll see Black-necked storks scurrying around for delicious lunch that keepers had placed when they slept in their indoor quarters. Cattle egret and Javan pond heron will stare at visitors that disturbs their fishing ~Ozzy
There are water dragons in the Australian bird walkthrough at Pairi Daiza: http://www.zoochat.com/111/australian-water-dragon-pairi-daiza-31-a-385351/
I'm surprised Intellagama can be kept outdoors in the climate (Piari Daiza, Belgium?) but one of the vivs at Arnhem has gouldian finches and beardies, and at least one Aus. collection mixed Chlamydosaura with cockatoos. Reptiles and birds go together species depending. My concern would be for eggs and offspring, both ways. More strictly insectivorous or herbivorous lizards ought to go with small hardbills and nectivores from the same environment. Intuitively. As long as the lizards can't access nests or prey on the birds. (A lot of agamids can prey on surprisingly large small tetrapods including their own species.)
There is one terrarium in Burgers' Bird House houses gouldians with blue-tonged skinks, but there used to be bearded dragons (and maybe the T. rugosa as well). Rotterdam used to keep timor zebra finches with their komodos, but there was a problem with that too (bacteria from the birds' feces or something).
When I went to Arnhem, the dragons were there. However I heard of a beardy eating a Berber skink (no notes on size) so I doubt they're entirely safe with birds unlike ie. the New World basilisks which are frequently kept with birds or small primates. Some lizards that eat insects seem triggered by insect-like movements, others simply by movement and prey size. Even giant day geckos will eat smaller lizards for example.
There are quite a number of Varanus-species in Australia but Varanus exanthematicus isn't one of them - he comes from Africa ! Anyway, there are several dwarf-species of Varanus but evenso I don't think they would be a good mix with birds. From the lizards you mention I would say Tiliqua would be the best candidate to be mixed with smaller seed-eating birds ( Estrilds, doves, parakeets ), Australian softbills are very rarely kept outside Australia and the only species kept in some numbers ( Kookaburra and Australian magpie ) would be a bad choise for most small / medium-sized reptiles.
Works fine with skinks and perhaps bearded dragons. Ideally with larger birds but finches and skinks should be ok. Certainly wouldn't attempt it with monitors, even dwarf monitors.
Coastal bearded dragons and cunninghams are kept with galah, princess parrots, musk lorikeets and various Neophema at Hamilton Zoo in NZ. Water dragons are kept with all sorts of finches, doves and neophema at the Whitford bird park here in NZ aswell Auckland Zoos new enclosure keeps Water dragons, king parrots, snake necks, musk lories and crested pigeons together. Ive also talked to many aviculturists through work who either keep beardies or water dragons with there birds provided there enough room. In terms of species I wouldnt use Id use birds that keep to them selves. Wouldnt use Varanus at all.