You dont even need to use rgb blend maps.. you can simply use the alpha channel of each color texture to blend... this way you can have 8 textures blended...it's a bit more tedious to make your terrains this way, but really.. how many terrains will have in your game.. not hundreds...

In a simple dll you can load as many textures as your card can support, but then you need to render the terain yourself..

Wouldn't it get messy though having the texture's rgb tile, but have the alpha map stretch as normal? That's always been my issue when working with multi texturing.

Well you would have to sample each alpha channel seperately, yes.. this isnt so bad on a fast modern card.

I found just a colormap with an alpha map and 2 detail textures worked very well(of course this depends on your shader or FFP scripts blending methods, FFP is alot more limited in blending options, heh). By using detail maps instead of full blown textures you gain the ability to use the color map to a good degree of variation, but you lack the color clarity the real textures give you(but lose variation unless you have over 2 textures, which can be slow). Though since your using terrain, this might not work. The levels I use it in are split up into sections so I can have different detail maps for different sections(think stone, grass, sand, road, ect.). With one large terrain it may look a bit bland with only 2 detail maps for the entire level. Keep in mind things will start to slow down once you add more textures, and always have a way to tile each texture differently(the stone doesn't always need to be as high res as the grass).