There was much talk a couple of years back about re-wilding – a suggestion to establish a plausible facsimile of the Pleistocene fauna of North America by introducing carnivore and herbivore species (including wild relatives of livestock) from Africa and elsewhere to the Great Plains. ((Check out a recent interview with a proponent. There’s even a Rewilding Institute now.)) But perhaps Europe might be a better candidate for this kind of thing.