It would be neat to be able to have fewer key frames and better in betweening so that more storytellers could have access without a team of CalArts grads. That doesn't seem unreasonable given what we've already seen, but I'm neither an animator nor an AI expert so I'm curious.
That's got nothing to do with AI, it's just economics, and it's been like that for years. Everybody doing animation on the cheap wants to avoid drawing every frame.
Prior to digital animation you used other techniques, like recycling frames or tracing over existing drawings (Disney used to do this all the time in their films).
What digital animation really allowed to happen was 2D puppeteering, where you could rig puppets and animate them in two dimensions without having to draw the key poses or the in-betweens. Now we're at the point where the standard way to do 2D animation is via puppets, rather than any sort of hand-drawn (be it key poses or full tweening)
But as shown in the video you still need to hand tweak a great deal even if you don’t mess with individual frames. Suppose someone is jumping through a window, you need the sound of breaking glass to sync with the glass being broken.
Most or all top anime content is still hand drawn, even the in between frames.
Mind you there is CGI in these animes, but the frames themselves are still hand drawn. How else would you expect them to be done?
There's no magic here.
Cartoons can do it because they just use rotations, translations and skews, anime does not have that luxury. The pro is that, imo, when done right, anime is just beautiful to see, mesmerising even.