I think 2D has struggled to modernize and Grease Pencil is the innovation it needed. Here is a highlight reel in advocacy for it.
I believe it can accomplish interpolated in-betweening as mentioned here by Jarrett https://www.youtube.com/watch?v=2DSnKa--aMM=222s
Here are a couple deep dives into the GP tool by some of the best independent creators using it currently.
Worthikids Blender 2D Animation Tutorial
GP hasn’t even reached its final form yet.