Is there any non-plugin solution to add template meta box on the category edit screen? Template meta box like that on the page edit screen, but this one for category. I'd like to have this function built into the theme page. Something similar to the one Mike Schnikel did for Scott B here.
I'm currently working on a theme framework and one of it's classes is a custom category template class which does just what you are asking for: it adds a select field to the category edit screen that lets you select a template, just like with pages, and i just published it as a plugin
and if you are not up with using a plugin then simply take a look at the plugins code which is a single class that you can even use from your functions.php file.
Here is an example of adding Meta to Categories, you can style and choose the input type