This combo’s very useful in 2.79 as it allows you to see the mesh under the armature but still have the armature display ontop of the mesh and be nicely selectable. Seems there’s an incompatibility with proxies, as they display a wired version of the armature in the same place as the proxy armature, making selection difficult.
Display as: wire also doesn’t seem to display the armature as a wireframe when in pose mode, it’s still mostly opaque.
Whilst I’m at it I’ll throw in that there seems to still be no good way to select all the bones of a single armature whilst keeping several in pose mode.