With the help of the amazing examples of Patrick Murris I have been able to connect a map from a GRASS workspace to be automatically visualised and tiled for WW.
The funky thing is that while tiled, a cache is created, so it is slow only the first time.

and the same with transparency:

I am still looking for a way to substitute the elevation model of WW with a custom one on the fly.
For now this is all about prototyping and documenting, but it looks great.
Would be good to have it embeded in JGrass/uDig as its default 3D viewer?
Who knows... :)