I don't have an opinion as to whether it should be a plugin or part of the core FARR, thats is for mouser to decide the best way to do it (if he decides this is a worthwhile addition).
From an end user's point of view I think the ideal would be to download a package which included the alias, css file and javascript file all in one go. I guess it would also be nice if the package could contain more than one set of alias/css/javascript files together. In addition DCUpdater would be able to update the package replacing the CSS/Javascript files if, for example, the layout of the webpage changes.