MorphOS could do well with "doing like Apple" and just hook onto some BSD (DragonflyBSD would be an obvious "amigan" choice, and also "just AMD64").
Where's the fun if you don't do it yourself, though?
Maybe MOS team won't admit it, but I'm pretty sure it's only really fun the first or the first few times. Like the first time ~selfmade PPC hardware (Pegasos), first PowerMac, firsttime Laptop (PowerBook). But much less for 2nd PowerMac version, 3rd PowerMac variant, 4rd PowerMac, 5th PowerMac variant, 6th PowerMac variant. Otherwise if it was so much fun it wouldn't have taken so long for all these although they are all PPC motherboards.
And even if MOS ran on top of some other common kernel instead of running on top of Quark Kernel, you could still make your own drivers for pretty much everything like disk/usb/gfx/sound/network if you really want. And if you don't tell anyone, MOS users probably would not even notice. Of course if later they find out, they will retro actively declare it a POS and stop using it.