I am not 100% sure I know the behavior you are after, but I might have something for you that comes close. It is the 'Find Files' tool. While it doesn't update results instantly, it does let you do some pretty powerful file searching across the entire Matlab path (or any other set of folders).
It's especially useful for finding code that depends on one of your functions.
Also, if you have a script or function that is on the path, you can start typing the name in the command window and use tab complete. You can do the same thing with open (this doesn't always work).
I believe open grabs whichever file which returns, so if you have overloaded file/function names, it doesn't work as well.
Hopefully there's something useful in there