Full automation of in-betweening was achieved during the 70's, I was there, it was a big deal, and then nobody used it. Interpolation animation, splines and vector morphing are all versions of that tech. The automation is in-betweens is how modern animation software works, but a lot people want 3D characters, 3D views, and the freedom to change perspectives after beginning. So "in-betweening" is now used more for the creation of certain motions that either cannot be motion captured, or are some signature motion for that character and the motion is designed - and that will be in-betweens for the motions between key poses, but those are all 3D motions, so different views can be chosen later. Even if the final production will appear to be 2D hand drawn, it is 3D production beneath, and our original in-betweening method at the individual joint level within an articulated body.