I did get the point of your suggestion, but you did not get a point of mine.
You will not have sufficiently good interpolation, if your UVs are defined only at landscape topology vertices. Interpolation is linear.
Well, what you would call good enough then? One way or another, you need to do that. Not sure what would be not friendly in having WPO doing this for you. Even more to that, I would prefer this to anything hardcoded.
You can calculate the exact amount you need to push the vertices up with distance, to account for vertical error of landscape and always stay sufficiently, but not more than enough above the landscape at each lod level and transition regions.
Surely you can add a ton of code to tie together landscape LODs and special category of mesh decal material, that would be automatically fed information about landscape LOD settings.
That can be done and would be welcome, but bothering with that is never worth the effort just to make it artist friendly, considering that anyone several months familiar with the editor can do it and especially if you consider, that you can just eyeball the distance required.