I was looking into modding the other day, specifically on adding and creating custom models and animations or editing existing animations. Found out rather quickly why it is that the animations in the game are all pretty terrible and stiff-looking, the Vintage Model Creator makes it especially hard to make animations, and it feels more akin to something that would've been used back in 1998. Using rigged meshes should've been implemented forever ago instead of whatever this is.
My suggestion is to completely replace the current model and animation system to support custom meshes with bones for animation via Blockbench or Blender. Having full compatibility with these programs would go a long way in making the game better, and making the modding experience less of a pain. I know this would likely be a big task, but it'll be well worth it.
A very good example of this compatibility is Hytale, they have native compat with Blockbench through a plugin and that makes modeling and animating less of a hassle, since Blockbench itself is already a very good well-rounded program with modeling, texturing, and animation tools built-in. Let's be objective here, the current system and program makes it a massive pain and is very unintuitive.
I'll even volunteer to remake all animations from scratch using these programs if implemented (shameless plug).