> I thought that the MorphOS closed source concept is built around some
> common closed part (OS kernel) and other parts can be solved by drivers.

Yes, drivers for plug-in hardware and peripheral (on-board) controllers could be written by third parties (and have been in the past). However, making MorphOS boot on a yet unsupported SoC with yet unsupported CPU core (and potentially unsupported controllers like RAM and PCI) obviously requires access to the OS kernel source.