Oh hey, someone linked to this thread so I'm dropping a note in it.
I did in fact get somewhere with this, but then real life intruded hard. To fill in the background a bit, I was toying around with Fractal Terrains, got something I liked, tweaked it a fair amount in FT, saved some grayscale images from it (land/sea mask, bump map, climate, temp map and precip map), futzed around with the bump map output in Wilbur for a bit, then successfully utilized the land sea mask to get a coastline (land/sea mask = blend shader input) and the futzed-with bump map to tease out some procedural mountain ranges (blend shader input again). When I left off (lo, these many moons ago ..) I had something going with this, though I'm really still at the beginning.
I won't have time for this for some time (hey look, English can do tricks!), but here's nibbles of what I left off with.
Cheers