Displacement amount can be animated and dials added, but that doesn't do anything for combining displacement maps at all.  It's possible to combine maps by hand and then animate the blending amount and then rename the dial (automatic naming is pretty bad), but that's something individuals would have to do themselves and wouldn't be very distributable.  That is, I could distribute my .cr2 with all of these hacks, but that wouldn't do anything for a third party wanting to use my displacement maps with yours.  So not extensible, which is extremely limiting when it comes to basic morphing properties.   And, testing, I'm finding material dials behavior to be spotty at best.  I just dialed it up then did an undo, and the material didn't respond at first.  Clicking on the amount made it revert to the right amount but the preview is still wrong.  It seems like the relationships among the dial, the shader, and the preview aren't exactly stable.