My apologies if this will lead further OT, but I don't think that your idea is as promising and productive as it appears to be in the first place. I once attended a very interesting university discussion on this very topic. The bottom line:
"Normal" zoos are actually not the best place for the ex-situ breeding of endangered amphibians. The chances of interspecific disease spread is higher than in specialised facilities due to housing / showcasing various species from all the over the world in one place. There are not a lot of zookeepers who are truly specialised in amphibian care. Most are trained to work with mammals and birds; amphibians are not really their focus, as, with a few exceptions, amphibians do not rank highly in the "zoo hierarchy". To decrease the likeliness of disease transfer, you would not only have to house the endangered amphibian species completely separately from the "common" animals, but you would also need a specialised staff that should not intermingle with the "normal" staff. Some endangered amphibians have high husbandry standards that require high quality technology and people experienced in using that correctly. I doubt that most smaller zoos could afford this on a permanent base, especially for a group of species that are not really crowd pleasers. Furthering local in-situ amphibian conservation on zoo grounds and beyond might be more doable for zoos with a tighter budget, but this also needs people in charge who know their way around amphibians.
I am well aware of the issues regarding keeping amphibians in captivity. I have read quite a bit about it, and one of my close friends was a very well respected herpetologist. That does not mean zoos should not do more to help. The opposite, in fact.
Nor did I say individual zoos need to house multiple species of amphibian in one location, because, as I am also well aware of, disease is a major concern with amphibians. It's the major threat for many hundreds of amphibian species. In fact, individual zoos focusing on an individual species is probably ideal in many cases. Yes, it's true that some species have perhaps developed some resilience after being decimated by the chytrid fungus in the wild, and that wild individuals who are in populations that were previously decimated likely have better survival odds than captive bred releases, but that does not mean ex situ conservation of these amphibian species should not take place, nor does it mean zoos should not be involved.
It's not about whether zoos are the best places for ex situ amphibian conservation or not. We don't live an ideal world. It's that amphibians, and many other animals and plants, need all the help they can get. Even if an individual zoo can't help out directly, they can still do more to connect with conservation. I'll share this, too:
The inadequate global zoo response to the amphibian extinction crisis
Connecting back to the thread topic, I think if the trend of mega budget exhibits is going to continue into the future, then those mega-budget exhibits should be more connected to conservation, both in situ and ex situ, whether it's small species like amphibians in a reptile house or rainforest or native animal area, or whether it's an exhibit focusing on larger mammals.