Just read a news story about a conference on Ted Turner's ranch in New Mexico. Somebody proposed putting large African animals in preserves on the prairies, which would replace large animals in the Great Plains ecosystem such as the sabre-tooth, mastodon and dire-wolf, and others which haven't been there for some time now, with lions, elephant and so on. Sounds like too much of a good thing to me, why not start by allowing ordinary prairie species, such as bison, wolves and bears, to repopulate deserted farmland? There would be enough problems in human/animal interaction without going further than that. At some point these proposed free-range zoos would abut on farmland or towns, and present problems with bears and wolves would multiply. So why not keep it at that level, after all wolves, bison and bears roamed the plains in the recent past? If you have space for exotic large animals, why not for indigenous species first ? The argument that people would pay to see them is a little weak, and would directly counteract efforts in Africa to preserve these species in their native habitats, and to earn tourism income by people in the third world.
If the objective is partly to maintain the plains as grassland by introducing elephants to destroy trees, there are two answers; first off , bison grazing do a pretty good job of preserving grassland as such and secondly people do a fine job when it comes to getting rid of trees. Allowing bison and antelope to multiply on deserted farmland would soon show economic benefits , as they can use the available fodder far more efficiently than cattle, with less care and cost.