You may be interested to note that Motorola designed the PPC as the natural successor to the 68k family. As far as Moto were concerned, the 68k series came to an end when the 68050 chip melted. It was only after the release of the PPC that they went back to the 68k and had one last push with the 68060 chip.
However, it had reached an end because apple (their biggest desktop customer) had gone PPC and with commodore dead, the 68k series was no longer a viable option.
So, to me, the PPC is the natural successor to the 68k family.