Using a heightfield shader on a globe is simply not feasible at this point due to projection issues. Heightfields are meant to be a planar representation, they don't work well with spheres. Use procedurals for best results, possibly (partially) directed by image maps in spherical projection. You can use blend shaders to vary your terrain features and blend between different areas. For water you could use a merge shader controlled by a large scale Power Fractal with one input being your entire terrain network and the other being a constant or water wave shape power fractal.
- Oshyan