Nice writeup. We implemented something similar 5 years ago and called it the Bridges Pattern, which did a redirect to the new system if the config data had the feature marked as "ported". We need more articles written on how to safely refactor legacy code. Most developers won't get to work on greenfield but it is much more sexy and fun to write and read about.
Thank you for the very kind comments. I agree that more articles on how to update/refactor legacy systems would be awesome!
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