Steps

• Register a new node, let's call it FooNode
• Create a new Katana scene and use the node inside
• Save/close
• Now prevent FooNode by being being registered. Or by using the env var or by just removing it from the init of its package.
• Reopen the scene previously created
• The FooNode instance will still be here but is not "dynamic" and just baked as XML in the scene, the purpose of this ticket is to warn the user that this nodeType is not registered with a visual indication.

To ease the transition to the katananodling workflow, we would need a tool that allow users to start designing their node in Katana as usual. And once satisfied just run a script that will convert it to python code so it can finalized as a BaseCustomNode subclass.