What I've seen in the video that vaio posted, that is already possible within GS, but it is different to what you were asking for.
You are blending the animations of the whole body, in the video of vaio there is the combination of animations of different parts of the body and adding angles and/or directions to some of the bones.
In the video that you posted in one of your last posts the blending from run to stand should be faster, that's all that you can do with this sort of 'full body animation blending'.
I understand your request, though.
I guess a function where simply put in the percent of the last animation could make sense, because most of the time, one needs blending from the last animation to the current animation. Maybe, additionally the function needs the animation speed of the last animation sequence as well.
Then the function would look like this:
ent_anim_blend(my, current_anim, current_anims_speed, ANM_CYCLE, anim_blend_percent, last_anims_speed);
Probably, one could build such function from Rei Ayanami's, I didn't have a close look.
