My "Idea" is that CA implement any form of file versioning or change control that would allow an administrator to force clients to pick up the changes to .js files without user's needing to clear their cache manually. This would be similar to the way SC form caching is handled. Without this it becomes difficult to effectively manage common custom functionality that isn't provided by the tool.
Any updates you make to this .js file are unlikely to be picked up by users in a timely manner. Therefore you would have to announce any changes so users are aware of the change, and can fix the problem by clearing their browser cache which also fixes 95% of Service management issues. Unfortunately this could drag out for months as some users don't frequent every form.