Well, Morphos would have to have the Amiga OS4 APIs added to their Abox. As for the other way around, it basically the same thing, have to add the native Mophos APIs to AmigaOS. I assume there may be more to it than that, it seems essencially what would need to be done. Unless you get into emulation or porting OSs. We'll just have to wait and see.
I see both going their own separate ways after a time. Like after both have established commercially released consumer products.