Thank you for the refresher, but we know what terrain LODing is.

My point is that you've been pointed towards several techniques already that fit your criteria:

For the terrain rendering, I prefer clipmaps. The chunked LOD algorithm is still in use in various applications, especially if they download chunks through the network connections. There is also some hw tessellation methods, like this included in the DX11 SDK. Or if you need a pixel-precise rendering or there is a triangle-throughput limitation (hi-resolution screens), the usage of ray-cast methods or hybrid ones may be a preferable solution. However, there is a problem of fetching data. Nobody can convince me that there is a better method than clipmapping for that for the terrain without holes or overhangs.
So look into those. I like the clipmap idea, but I personally like the idea of using hexagons rather than squares.