There doesn’t appear to be any way to track the usage of the custom node. While I appreciate the custom node versioning features, it gets very confusing when creating a new version to fix a bug in an old version. Particularly when I have to go through all of my workflows to find every instance of the custom node to update it. I would appreciate being able to at least view which workflows are using a custom node (like you can with endpoints and pages)
I agree this would be an excellent feature. Our engineering team currently has a ticket open for this functionality, I have given it a +1 for you and will follow up should this be implemented in the near future!
Please let me know if you have any further questions.