Well, that's the minimun they need to do. I even think they should have made that island smaller in order to give more space to the hoofstock. About rhinos, I really doubt they are gonna be held in the same area. Nine giraffes, zebras, wildebeests and impalas would be ok, maybe, but rhinos would by no means fit well in an exhibit of that size. The whole complex is like 12.000 sq meters (more or less 3 acres) but the free area (that is not occupied by the island, the river, the path, the handling areas and the hippo exhibit) is only 4.000 sq meters (1 acre) wich would be quite small to hold such an amount of megafauna.