As of 2.79, i’m afraid you still have to use Shrink/Fatten to scale faces along the normals while staying on 2 axes. Take a cylinder for example (no caps) and select both edge rings and try to scale them with the Settings:
Transform Orientation: Normals
Pivot: Individual Origins
The result will be convex/concave and includes the Z-Axis instead of just X+Y. While Shrink/Fatten or Extrude Region (vertex normals) will do the job, you have to uncheck the Z-Axis manually in the scaling options. I’m afraid if there is a reason for it, a limitation or just a bug ignoring pivot + orientation? I often stumble across it since it’s breaking the usual tool workflow with just shortcuts a bit.
I attached a example. Thanks for your answers.