a year or so from now after I have finished fully integrated and bugfixed the materials system, someone get me to make a tarain engine for FS, I have some good ideas for one. I'm thinking useing a radial subdivision of the surface and updateing it every two or three seconds (would be better if it could take advantage of multi-threading) based on the player's position above the surface. the idea would be rather than a square grid your have the point directly below the player on the surface act as the center of a bunch of concintric circles with axiese spreading out acting as a polar grid, width of the circles and number of axies would be a function of altitude.
I've never seen this sort of implementation performed so I am quite interested in how this idea would work out. but I think it would provide the absolutely best method for both getting the most amount of detail near the player and culling unneeded geometry from rendering.