Sadly it's just a dream to create something in the DOM and make it private, if we ever get there, we will go to mashup heaven.

The ability to limit the scope of a script tag would be desired too. Something like:

<script> var notsoglobalobject = {}; </script> <script global-object="notsoglobalobject" src="yourevilscript.js"></script>

But stuff like these are both hard to design and hard to make real standards.