It would be so good if OS X and iOS became one unified operating system at the base level, meaning that applications etc are universal across both. To do this without messing up the great way Mac works now, apps built for iOS which have flexible size guidelines could just be run as windowed applications on the Mac, meaning the great app store ecosystem of iOS could come to the Mac. This would probably also be better on Apple and developers end of the deal as they could update their apps for...
macOS and iOS unification
macOS and iOS unification