Articulation history dump time!
So, nothing about this doll--not even the MTM articulation--is original to Mattel. Some sixthscale action figures have had that level of body articulation, as well as fingers articulated like that, and articulated toes, in the early 2000s (and the Busy dolls only had moving thumbs--I'm not sure how much room inside the hands the thumb movement took, or if it would work well with the room needed for the finger hinges, without leaving areas of extremely delicate plastic between)
Here is a hybrid I did in 2003, grafting the feet from a DML action figure, with articulated toes, onto a body that originally had shoe-shapes that you covered with cloth "boots" instead of feet
I know the quality isn't great, but you get an idea of how toe articulation looked
Oh, and, the 16" Madame Alexander Alex dolls also had articulated toes--I don't have any foot photos of the articulated Alex dolls I had, but I did find an eBay listing showing the feet
Here's a picture I took in 2002 of a GI Joe with what Hasbro called Gung Ho Grip, with the fingers on a hinge
The index/trigger finger was separate from the rest, which were cast as one piece. I remember some people very carefully cut all the fingers apart.
The body on that GI Joe had the kind of articulation that was called super articulated back then, and most doll people think of as MTM now. Here's a current eBay listing for the guy above, out of box and out of clothes
(Yes, he's supposed to be WWII war correspondent Ernie Pyle. No, that physique is not at all accurate. That was just the standard GI Joe body. It was also very short.)
Larger fashion dolls have hands and feet that are about the same size as sixthscale action figures, so the finger and toe articulation can directly translate from a sixthscale action figure to a ~15" doll, but, putting this kind of movement on a sixthscale fashion doll's significantly smaller appendages might be too delicate (and or fiddly) for mass production, especially at the cost-cutting levels everyone is yelling at Mattel about these days.