Let's explain the positive effects of hybridisation: instead of decreasing the genetic diversity of a small group by even carefully planned inbreeding, why not fuse the small with a healthy, only minimally different, yet compatible larger group. This will not only result in an increase of the overal genetic diversity due to new genetic material brought into the larger group, but one benefit might be a positive heterosis effect, i.e the hybrids might be healthier & better adapted to the Northern whites' habitat than pure Southern whites - or heavily inbred Northern White Rhinos. Example: Peregrine falcon reintroduction in the Eastern parts of the USA.