Jink does have a 2D engine inside it with an editor along the lines of spine. Spine is far more polished however and looks like it's got quite a good uptake so I think I'll add a plugin myself at some stage since there's now a public format for 2D armature animations!

Does spine allow you to reference your source images by filename or does it pack the data with the json/binary? for example if I were to use spine I'd keep my support for vector formats such as SVG, so not only can they be part of an animation but that animation can then be resolution independent.

it's a damn sight easier than handling 3D formats! I'm still having issues with MD5 quaternions in bone space and IQM rest poses