Australia has already seen the effect of some large herds of ungulates roaming around their native vegetation. I read somewhere that the largest herds of "wild" (i.e., feral) camels are in Australia. Can anyone confirm this? There are also herds of water buffalo and several species of deer (Monty discusses this on his recent photos that he posted).
From reading the article it sounds like what the zoos want to do is establish a large facility akin to the San Diego Safari Park or Whipsnade, but probably without visitors and with larger enclosures.
Regarding demographic winter, I am a diehard optimist that parts of Africa are going to remain wild and other parts in time will be restored as standards of livings rise. The U.S. went through a similar transition in the early-mid 20th century. Deer and waterfowl populations were driven to very small sizes. As standards of living increased the populations urbanized, the food supply became stable so people weren't needing to eat wild game, people moved to cities, and populations of animals started coming back. It is entirely possible that I am wrong about this.