Okay, I agree with you and I thank you for your feedback.
However there are some things to consider:
As the characters differ in size, bone length and other things, people would have to adjust the parts first to match the animations.
Most animation packages already offer said customization easily.
Let's take the example of the wizard girl holding the axe instead of the staff, the glow effect of the axe would have to be repositioned onto the axe, as the axe is a lot shorter.
You can pin the effect to the axe. In fact, most effects can be done better with OpenGL/DirectX directly in the game engine instead of baked animations, so pinning the effect becomes even more desirable than precompiling.
What would a character pack consist of? Only the precompiled sprites together with the source files of the skeleton and the animations? So you would have to purchase another character that wears an eyepatch if you want your toon to wear one? Or would a complete character consist of all possible parts applicable to him, already resized and worked into the source data?
The character pack would consist of the skeleton, animations and parts in the form of spriter/spine source files, as well as precompiled sprites, each on a folder, in PNG format.
If you want to mix and match characters, you have no choice but to use spriter/spine source files and resize/position them yourself. This shouldn't be hard for a game developer - programmers' difficulty lies in actually drawing the parts in the first place. Of course you'll need to put some effort into making sure parts are universally cross-compatible (ex: all hats should fit all characters).
(Of course the would have to be various different attack animations for each toon, as you cannot stab with an axe, compared to a dagger,...)
I discovered a kickstarter project named "Indie Graphics Builder #2":
The characters can only be composed of different parts because they have all the same basic doll with the same shapes and sizes.
There's nothing stopping you from using the same "doll" in your project as well - in the form of a base sekeleton. This way you can include animations for stabbing and swinging to the basic skeleton and apply said animation to all models.
If you want bigger and smaller characters you can do that too, so long as you keep the proportions the same. Some animation packages are smart enough to apply animations to skeletons with different limb sizes, you should probably look into that.
(Also I'm a backer on the kickstarter you mentioned. He's missing exactly what you're offering).
I really love the idea of heavily customizable characters, I just don't see how this could be done for high-res sprites of that kind.
I don't see how resolution is an issue.