Im not so technical guy, but it seems that technique is not called weight blending.. you can read here about it..
No weight blending really looks different, if you put hardness to a minimum you'll see the result is almost the same as the video. Previously, the materials just lay on each other, now it looks like Vertex Blending
But splat maps, I also really want, in Lumberyard it was added a very long time ago
And cryengine have this for ages.. you can read in docs about it.. .. http://docs.cryengine.com/display/SDKDO ... yer+Shader