I am developing a little utility to help with theme translations. It takes a po file from a translation-ready theme and it translates the strings which it already has in the database. The purpose of this is to cut the work of translating the same strings in different themes over and over again.
Now, the way I implemented this is I used a page template, the reason being that a. WordPress generates a clean URL for me; b. when the page loads the WordPress is already loaded and I can access the translation API, and I can manage it within WordPress: It's not a lonely php file somewhere in the server.
Also, imagine a developer builds this super awesome landing page plugin, the cleanest way to provide it for the user is using a page template that the user can choose which page to apply that template on.
Also, imagine the example sections of css-tricks.com. All the example can be a child page of "Examples" parent page (and hence a clean /examples/whatever url), and each could use a page template that has just the common layout and the advertisement codes. This is not tied to the theme.
The only workaround I could think of was using the template_redirect hook to check for the current url and spit the custom page template if it matches. Ugly.
I also tried overriding the 'Page Attributes' meta box so it uses a customized version of get_page_templates function, which works, but the same function is used for quick edit functionality in WordPress and I couldn't figure out how to override that. An ugly solution nonetheless.
This was one long post.