I have been using Flash to export. It works, I can export a PNG sequence. I just have been looking to get if off my computer. I don't think onion-skinning would be THAT hard to implement, as I use like three free iOS animation apps that seem to have that feature.
I've considered using Inkscape for drawing and just utilizing the layering system to onion-skin. Does anyone know of a way to import SVG graphics to C2, or do I have to rasterize first?