A number of Stack Exchange sites have specialized support for non-standard types of post formatting. For example, on Japanese.SE we have some custom JavaScript to add ruby to our posts. We've used this all over our site, and without it the site will essentially break.
Since site customization is being reduced, I'm nervous that these might get hit with the feature removal bat as well. Could you please reassure us and let us know that these site-specific customizations are not going away as part of the redesign?