Setting up real displacement in 2.8 I've been struggling to get a height map to be displaced in a plane. I'm trying to do what is done so nicely in this answer, and in fact, do it with a variant of the height map in that question, which was also me. 

I have now tried 2 approaches with 2 planes, both of which are in the attached file. The planes are UV unwrapped.The first approach was to add a subdivision surface modifier, and a displace modifier with the height map image as its texture. 



The second approach was with a shader. It plugs the color data from the image texture from the height map into the Y axis of a Combine XYZ node, and then plugs that into a vector displacement node, and from there into displacement on the material output. 



Neither method is working. For both planes, Displacement and Bump is selected under Properties > Materials > Settings > Surface. Cycles is the render engine. What is wrong here?
Everything works fine.





But you forgot to choose a UV for modifier approach



and used a wrong setup for shader displacement.



Also you'd better re-export your height map as OpenEXR or PNG 32 bit otherwise the result shall be jagged.




Your example file on developer.blender.org works fine too.