I like the thought process, but I think Marshon is having a good year. I know he's about to get expensive, but he's one of the things right with the Saints right now.
He's at the back half of his career, still has good years left, and his high level of play gives him real desirability. His contract makes zero sense for the Saints with their cap issues and depth at CB, but a potential playoff team looking to shore up their defense? Look at the Commanders. They could be 7-2 going into the trade deadline. Their defense hasn't been great, but adding a top flight corner still in his prime would give them a big boost, especially in a very weak looking NFC East. Washington also has a ridiculous amount of cap space this season and beyond.
The Saints get much needed cap relief and a solid draft pick. Washington gets a high level corner to help what is looking very much like a playoff team.