While it's a very interesting idea, currently we don't offer a generic animation and character library in the way Mixamo does.
What we already have to offer is the Spine Hitman and Gunman asset packs, which provide a flexible rig with animations, where you could just create your own skins to replace the existing ones.
Spine: Asset Packs
This is true for any Spine project, where you could replace the existing Skins with new ones.
At least from my programming standpoint I'm not sure a generic animation library would work, as the used camera perspective plays a vital role in how the rig is actually setup. A 2D character rig is very often asymmetric to some degree, e.g the front-facing leg hits the ground at a lower position than the back-facing leg (either due to perspective or to the camera aiming downwards). Here a standard 3D character rig has the advantage that everything can be more easily retargeted, since the left and right legs are always on the same ground level.
