I know nobody that reads this blog probably cares about this (ha! I assume someone reads this blog!) but I just became familiar with the concept of "Pleistocene rewilding" and since I was lamenting the Pleistocene megafauna myself just recently, it seemed an appropriate add-on.
Rewilding is the concept of reintroducing species into the wild where they've gone extinct locally. The best example of it is when wolves went extinct in Yellowstone. The local ecosystem was thrown for a loop, wolves were eventually reintroduced, and the local ecosystem eventually returned to a relatively stable scenario. Of course, a Pleistocene rewilding is much more significant than simply reintroducing wolves into the American southwest or whatever. How do you reintroduce sabertooths and mammoths when, of course, they're already extinct?
The answer is: you reintroduce closely related proxies. The Pleistocene rewilding starts with reintroducing and protecting some extant species into areas where they no longer live: some examples would be reintroducing grizzlies, pumas, wolves, bison and pronghorn into more southerly areas. As proxies, they've proposed lions, cheetahs, elephants, onagers or kiangs, Przewalski's horses, zebras and camels into the same region.
Workable? Almost certainly no. Problematic? Yes, on so many levels. But a fun and fascinating idea nonetheless? Absolutely.