Atm customization for Dump is highly restrictive and only works on customizing top level object. Converting it to Expando is next to useless for heirarchial objects as it results in significant loss of functionality (empty lists are rendered as objects with Count/Length property vs "(0 items)" string as in default Dump version, sub-objects don't get properly rendered.

What might be much better from customization point of view is ability to customize Dump via a visitor pattern. For each property (node) in object graph, you would get a "VisitMember" callback with it's property type and value. At that point you decide how to render it (you can check which type it belongs to via reflection to make decisions or skip it's rendering entirely). This would allow for nested visualizations to be customizable at every level, as well as overriding "built in" low level visualizations for basic types like strings and integers.

Roslyn's visitors are a good example of the pattern I'm proposing.