Great news about the C3 runtime beta plug-in! Thanks a lot for that!
I've finally been able to switch to the C3 runtime thanks to it.
Bug report: I'm using a lot of transparency in my sprites, especially on the borders of the image, and the transparent areas seems to be blackened somehow. Here is an image showing you the correct version on the left (C2 runtime) and the bugged version on the right (C3 runtime).
Don't pay attention to the background which isn't 100% the same, just look at the black "outline" around the arm, hand, and every separated part of the scml object.
Thanks again! :)