currently, models can have a maximum of 8 skins in 3dgs. so 100s of skins can not be blendeb through shaders. u can fake it 2 some extent though....

create a nice huge texture with hundreds of blended textures in terragen...

scale it down to maybe 2048*2048. even at this size the texture resolution will be bad because of the terrains'size... to make the texture look better, use a tiled deatil map applied through pixel shader 1.1...
this technique works 4 me.. hope that helps