I was under the impression that Blu-Ray had already done this, creating dual-format discs? And I think they have the advantage in that their format supports more than two layers.. so you could have a dual-layer DVD
and a dual-layer BD movie on the same disc. Along with the film's soundtrack on a CD layer.
Maybe I'm getting it confused with the BD/CD hybrid.. like today's DualDisc format, but on one side, with BD and CD. But if they can do CD, surely can do DVD as well.