“Seriously. What Sony should have done is make DVD’s that would be read like a DVD on a DVD player, but read like a Blu-Ray disc on a Blu-Ray player. They had the technology years ago, but never did anything with it. Instead companies went with dumb double-sided discs or packaged a DVD with a Blu-Ray disc.”
BD has a different structure than DVD. You cannot combine BD and DVD. HD DVD had the option of putting DVD and HD layers on the same side of the disc but the option was not really utilized by the studios.
JVC did it way back in 2004, but unfortunately it never caught on.
I still think what they should have done is used H.264 on standard dual-layer DVDs instead of sticking with MPEG2 and pushing blue laser technology (which turned out to be a nightmare). Actually, the studios were pushing for exactly that but Toshiba successfully lobbied for blue lasers.