I am wondering the same thing myself.
What I have been doing (not fun) is
creating my heightmap in one of many free programs (or MED),
then converting it to a model, then texturing it with
GIMP (white gives me my road, blue gives me grass)
, but it is not really "WYSIWIG", so it is a pain to
work with. I can even see where the elevations are, so
I know what is high and low areas, because I paint over
the heightmap image.
I have "T.ed" The Terrain Editor, but lost my code....
that exports a blurry baking texture, but maybe with that
you can export the correct map, but I am not sure....
I know it can export "alpha map", so that could mean it
will do this, but I am not sure what that means yet.
Good news, I think Conitech is working on a real-time editor
with better terrain (PLEASE! this would help me!)
and maybe shadowmapping too....
-Jimc74