I agree that it would be great to have a botanical garden on Dix Hill. It is a much better site than the current site of the Raulston Arboretum, for a number of reasons: Dix has a beautiful landscape, with hills, flat areas, and a creek. The current Arboretum is mostly a large flat area, with no interesting landforms. Dix Hill is near downtown, near other attractions, and has great views. The current arboretum is in a light industrial area, next to the noisy Beltline, away from any other attractions, except of course for Neomonde.
But the Arboretum, wonderful as it is, is only partly a show garden. It is also a place for the Horticulture school to experiment with plants and teach horticulture. Beauty, therefore, is a secondary object, unlike the more gorgeous Duke Gardens. At the Arboretum, wonderful plants are sometimes pulled up just to make room for new plants the school wants to try out. And while individual parts of the Arboretum are nicely designed, there never was much of an overall design for the place.
Therefore, I believe that a Botanical Garden on Dix Hill would not replace the Arboretum, but supplement it, as a showplace for landscape design as well as horticulture.