About that I think with 5.3 there is something done in that department you can now import big files for landscape and it manages to chunk it as needed…
Oh nice you’re right:
We updated landscape import/export to support very large landscapes/resolutions by leveraging World Partition and splitting the import operation into several successive batches.
Then you could try to directly download the tiled heightmaps from here and import them in Unreal:
https://geoservices.ign.fr/rgealti
making a landscape material somehow aware of the color informations from a satellite imagery : shading and coloring ground and foliage so that from a distance it could simply display the satellite colors, and having it nicely transition to coloring meshes in a coherent way.
The landscape material in the plugin supports to have an “Overlay”, which can be satellite imagery, but it has to be downloaded externally (for example using QGis). Then you can set the transparency of the overlay. You could try adding a transition to the material using linear interpolation, between the overlay and the automaterial (using the distance between Absolute World Position and Camera Position).
I’ve added an issue to track this feature: Simplify adding satellite imagery and add distance blend transition · Issue #2 · LandscapeCombinator/LandscapeCombinator · GitHub
another crazy but fun idea would be to forget about landscape, that is leveraging the huge mega scan library and managing a “landscape 2 mega-assembly” process : using landscape heightmap information, Satellite images color information, reconstructing the landscape by assembling loads of nicely detailed meshes
how fun is that ?
Very fun 
But I wouldn’t be sure how to start! Could something perhaps be done using PCG? The plugin has a node to filter out point based on areas of interest in OSM (such as forests). So once the landscape is spawned, in your PCG graph, you spawn trees in the filtered areas, and you can spawn megascans cliffs either from satellite imagery or from the Cliff layer from the landscape automaterial.
By the way now that tesselation is back, you can have the geometry of the texture (for instance a cliff geometry) deform your nanite landscape (without the plugin).