I wanted to see if I can produce a multi target SceneKit project with SCNTechnique which supports both Metal as well as GL shaders. It seems to indeed be supported.
Targets include macOS, tvOS, iOS but I was not able to figure out how to attach the SCNTechnique object to a watchOS WKInterfaceSCNScene object.
The shaders apply a simple displacament map based on this tutorial and a simple alpha mask from an external image. I leanred how to add Metal shaders by browsing this repo.