From what I can see the default LE terain shader uses 16 textures, but you can't use all those for different stuff like rock,grass,snow,sand etc..
So basic RGBA blend is used here too.. I would guess with accompanying bump textures, and base color texture.
These are the textures fetched in terrain.frag :
uniform sampler2D texture0;// texture0
uniform sampler2D texture1;// bumpmap0
uniform sampler2D texture2;// texture1
uniform sampler2D texture3;// bumpmap1
uniform sampler2D texture4;// texture2
uniform sampler2D texture5;// bumpmap2
uniform sampler2D texture6;// texture3
uniform sampler2D texture7;// bumpmap3
uniform sampler2D texture8;// texture4
uniform sampler2D texture9;// bumpmap4
uniform sampler2D texture10;// basetexture
uniform sampler2D texture11;// tilemap
uniform sampler2D texture12;// colormap
uniform sampler2D texture13;// alphatexture
uniform sampler2D texture14;// normaltexture
uniform sampler2D texture15;//heightmap