Yes, while there may be some smarter replacement for hardware tessellation, Nanite as in importing extremely high poly meshes won’t be replacement for it. It’s just completely different use case.
For example you can use HW tessellation to tessellate up close section of like 4x4km landscape, and all it takes is relatively small landscape heightmap and relatively small tiling displacement texture. Small in terms of asset/game install size on the disk as well as memory occupation.
I am really having a hard time imagining importing actual landscape mesh at the detail density of sub-5 centimeters. At 4x4km with 5cm minimum detail size, that would be 12,800,000,000 triangles. Yes, 12 billion. Not only would that be huge, but just authoring such a dense mesh would be extremely difficult, and probably challenging to even display in any kind of rasterized viewport.
So the idea that Nanite is a replacement for hardware tessellation in all cases is just unrealistic.
That being said, not knowing much about nanite, I currently assume it’s basically alternative to static mesh actor/component. But perhaps nanite is more than that. Maybe the same tech that seamlessly gradually streams triangles based on the screen space visibility could be also used to dynamically construct triangles based on the camera view from low res input geometry and displacement map. In that case, it could indeed replace HW tessellation.