I am facing the same challenge when it comes to terrain LoD. Allot of things are bothering me when it comes to implementing this feature. I'm limited to -2000000 to 2000000 quants in world size. I need to save poly and using large poly size with detail map texture makes the terrain polygon shake so I have to eliminate the detail texture and use plain texture instead. I wanted to use my own terrain LoD but loading different LoD for each tile is slowing things down and I also have to work with each node's texture Lod. Haven't tried loading z position of each vertex yet but I'm wondering how to use it in a way that it would line well with other tiles.

Then after solving the terrain LoD problem you still have to figure out how to load and unload terrain entities which is I'm trying to figure out with the terrain problem.