Hi,
Mecanim is not replaceable by PlayMaker, they can work together, but that's about it. They are two totally different systems defined to serve very distinct purpose.
Mecanim is a dedicated Animation system to define animation states and so much more.
I think you are getting confused because they both feature a visual way to work with them using states, but they have very little in common actually.
Now, having said all this, you could create a PlayMaker fsm that would behave just like a Mecanim tree ( in essence, it's actually always the case basically), but it would not be able to apply/expose all of the Mecanim wonderful technics and very productive features to control animation blending and all. Essentially you would only be able to control legacy animations with PlayMaker this way.
Bye,
Jean