It doesn't matter if they coexist or launch separately. I don't know what they'd call it or how it'd work. What's important is to be able to use the functionality of both on one device.
That's what I've been saying. There's no need to have two separate OSs to get the optimum functionality. Using a dual boot set up (like you have been suggesting) implies two separate systems that don't crossover.
What would be more progressive and practical in the years to come? Having two separate systems in which Apple and developers have to publish software twice, for two different markets? Or one system in which Apple and developers can publish software once, to be used in both types of devices?