Considering the close proximity of the BTS facilities to the former elephant complex, it's not hard to imagine them investing in an additional exhibit there which could be connected to the BOH facilities via an overhead pathway, similar to Auckland's, just on a more extensive scale.Yes, @steveroberts is correct that leopards must be held in fully covered exhibits as per state rules (i.e. no open air exhibits). Historically, they’ve proved notorious escape artists across the world’s zoos.
Sri Lankan leopard are unphased by living in proximity to other big cats, so they could retain the 1992 tiger exhibit for Sumatran tigers; and build additional leopard exhibits around it. Importing a breeding pair of leopard unrelated to the pairs imported by Darling Downs Zoo and the National Zoo would enable them to supply other holders with unrelated males for their offspring; but ultimately it’d depend on availability through the EEP.
Depending on their level of commitment to Sumatran tigers, another idea which can’t be ruled out is Melbourne Zoo building an additional Sumatran tiger exhibit. Combined with their extensive BOH facilities in, this would see them well placed to import a breeding pair and establish themselves as a breeding hub.
That would mean they could utilise the enclosure in the Carnivores precinct for another species (like Sri Lankan Leopard), or even as a third supporting tiger exhibit to perhaps hold a surplus pair of cubs born.