There would be more and more extras (add-on) made by the community, and I hope so. Perhaps specific MODext namespace to accommodates extras will make javascript's extra more organized, and also to prevent conflict between one extras to another or with MODext.
MODx.extra or
MODx.addon would be a good choice. So, if I create a new extra named "gallery" that required ExtJS, my MODext would be MODx.extra.gallery.
Thanks
Note: I can't express my thoughts in English very well. Hope no one confused reading my post