For interlaced ... I have no idea. Depends a lot on how the interlaced images are stored, I guess.Yes, exactly. Until there's samples, I'm not going to worry about it.
There's also progressive JPEG. <http://www.faqs.org/faqs/jpeg-faq/part1/section-11.html> <http://en.wikipedia.org/wiki/JPEG> <http://en.wikipedia.org/wiki/JPEG_2000>