"publish_form_headers" hook exists, why not a "edit_template_headers" hook?

Moderator’s note: Moved to Extensions.

I think the subject title says it all, but… How come there is a “publish_form_headers” hook but no “edit_template_headers” hook?

Leevi Graham used the “publish_form_headers” to add the TinyMCE WYSIWYG editor to the Publish page and I’d like to take the same approach to add a better code-editor to the Edit-Template page.

I’ve been modifying the “cp.templates.php” file for my own uses, but I’d love to extend this by creating a proper extension for the community. I know about the “edit_template_start” hook but I don’t want to “completely take over the template editor”, I just want to drop some unobtrusive javascript in the page.

If there’s a way to do that using that hook, that I’m not skilled enough to know about, I’d love some advice so I can wrap this extension up and post it for the community. I can only guess that it can’t (or is too difficult to) be done since Leevi didn’t use the “publish_form_start” hook for his implementation of TinyMCE. Hence my initial question.

Thanks.