I can do most of what I need to do by overriding the feed template, allowing custom output by search term, tag, and category. However, getting an individual post for the feed (ie. using p= or page_id= query variables) doesn't seem to be an option by default.
What would be the best, cleanest way (ie. least amount of conflicts) to create the custom output post/page output? Simply add a new query_var filter and hook into parse_request, add new query vars for the feed somehow, or some other method to override the template for the content from within the plugin code?