I have been working on solving the issues involved with planet sized terrain meshes for a while now, and it appears that I-Novae has solved them: http://youtu.be/a6a69dMLb_k?t=2m59s
The main issues are GPU precision and jitter issues when using large values on the GPU and morphing LoD details smoothly into the next LoD.
It appears that I-Novae is using some sort of quadtree cubesphere, but the leaf node meshes are being done on the GPU to do the smooth morphing between meshes.
I'm not sure if they are even doing that, but I also don't see how it is possible on an Earth sized planet.
If anyone has any wisdom to share on the topic