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.