1. A lack of variation, even skin deep, is even less interesting than only skin-deep variation. That is often the norm in large "open world" environments.
2. Much of what we find most interesting about the world is, in fact, skin deep. Take humans for example; all fit the same mold, but the range of human variation is endlessly fascinating to artists and audiences alike. Similarly, the layout of the Prati region of Rome and the Marina/Cow Hollow district of San Francisco is not wildly different. However, both are distinct, worthy of visiting, and unlikely to be confused with each other.
3. Current methods of procedural generation, without AI/ML, already result in fairly interesting maps. Could "true" AI do better? Perhaps, but I'm not sure that the delta is so great that the results would be noticeably better than a well constructed procedural algorithm (play "Tea for God" if you have a VR HMD and a lot of space). I could be wrong though - the gold standard remains hand-placed, human-built worlds filled with little surprises. If an AI approach resulted in a level design competing with the best of bespoke worlds, particularly at a lower development cost, then I'm all for it.