Having compatibility to legacy software is a pretty upside. Either you use an application that runs power efficient, maybe the entire operating system uses the power efficient ARM at default and then for compatibility or for faster calculation (games?) the x86 cores could be used. Intel already does two different kind of cores, performance and efficiency cores. And smartphones have something similar too. I imagine this would be expensive and it is not for everyone. And who knows what other cutbacks and drawbacks it would require.
Having compatibility to legacy software is a pretty upside. Either you use an application that runs power efficient, maybe the entire operating system uses the power efficient ARM at default and then for compatibility or for faster calculation (games?) the x86 cores could be used. Intel already does two different kind of cores, performance and efficiency cores. And smartphones have something similar too. I imagine this would be expensive and it is not for everyone. And who knows what other cutbacks and drawbacks it would require.