Correct if wrong, 

my experience is, that a displacement map works in full 3D Space.

But only, vertical to the mesh: In and out relative to the mesh surlace.

if at all possible with R, G, B, values, one could mathematically speaking, have: in-out, up-down, left-right, again, relative to mesh surface.
But that would complicate things beyond . . . . ., even beyond usability.

Morphing points in-out, relative to mesh surface would be very uselfull and help the rooms calculate around this point displacement.

One could use the same "gray" map ond in this node only re-calculate, and effectively displace the points.

Poser 1, 2, 3, 4, 5, 7, P8 and PPro2010, P9 and PP2012, P10 and PP2014 Game Dev
"Do not drive faster then your angel can fly"!