It would be cool, but I can see a point of diminishing returns. If you kept it to say, two OS flavors or so, yeah, not bad. But the moment you go down that path, the abstraction needed to ensure both sets of binaries play correctly with the underlying hardware and still remain isolated and separate starts to eat into the overhead you were trying to save in the first place. It'd be cool to pull off, but I have to imagine that it'd be for niche applications.