The obvious next step is for Apple to do a Samsung, and have iOS and OSX running on the same device, with iOS running when the device is in portable mode, and OSX running when it is docked and connected to a KVM.
At some point there won’t be a separate Mac and iDevice line. All devices will be iDevices that can run both iOS and OSX.
Apple has clearly been pushing for this for a long time. They’ve taken so many steps towards making the transition when a user switched from 1 OS to another seamless, with technologies like iCloud Drive that provides a single file system layer, universal apps that work across OS’es, handoff that allows for a smooth transition of state for an app running on OSX to the same app running on iOS and vice versa, etc.