I recently started to spend time on my engine again, and have finally solved the issues with importing geometry and animations from Blender. There were some problems before that I had not noticed because I had not tested enough, but things seem to be running quite well now. I've also cleaned up the code a bit, and improved the export scripts, making them more user-friendly. The animation export script currently only exports single rig poses though, so the next step will be to export an entire "movement" in one go. After that I think I'll look at graphics again, try to throw in some fancy effects.
Posed bones. It may not be obvious, but this is supposed to happen.