I think that's a cool idea, but the bakers already tried that and decided that it was a major, major, re-write.
The strength of Cakewalk and Sonar on the Windows platform is also its Achilles heel as far as being ported to another platform. It is very tightly wrapped with Windows code libraries and much would have to be coded from scratch in another universe to get the same functionality.
A complex DAW app would need to be designed from the ground up for cross platform compatibility in order to avoid the re-coding necessary to make it work after the fact.
I agree that a cross platform DAW app would have wider appeal, but the technical issues involved with achieving that goal are not insignificant.