I think it would be great to see Asiatic lions in the US. The other subspecies that I think should be brought into captivity is the mountain gorilla. Even though the population is small, they are in a very unstable part of the world. It would also be nice if South China tigers could be brought in. I never knew that Amur leopards were all impure specimens in the US.
Mountain gorillas are benefiting from insitu conservation efforts and their population is actually growing. Considering the Western Lowland gorilla population is just now becoming sustainable in the U.S. there is no point in bringing in a new subspecies which will ultimately take the available holdings for any growth in the western lowland population in the AZA.
Surviving South China tigers are hybridized with Bengals. The entire recovery program if you could even call it that, should be far more intensive. Rather than one or two cubs every year or so.