We certainly need to keep the inDOM mapping for now - this guards against race conditions of loading a script twice. (A user hits two controls rapidly loading the same JS, this will make it only load a single file).

Regarding the DOM removal for JSON-P - it was something Rick requested, but we are not currently leveraging. The use case is, leaving a JSON-P application open which polls for data - you don't want the DOM to be filled up with script nodes and crash. It's a valid use case - but not something we really need to worry about right now, so I would be ok removing this.