Are you thinking to have at runtime or at edit-time? I ask because my IntelliJ plugin for Arc does this - you just hit cmd-shift-I (on a Mac, at any rate), and a little window pops up with the source code for whatever the cursor is on. Is this what you mean...?
I was thinking at runtime, I.e. in the repl or available via the online help op. It would add greatly to the automatic documentation that currently exists.
