page-template-state.php

<?php

/* --------------------------------------- */
// Show page templates as states in page list
add_filter( 'display_post_states', 'prfx_template_state', 10, 2 ); 
function prfx_template_state($post_states, $post){
    
    // Fetch array of templates, returning Display name => slug, which is odd, but useful.
    $templates = get_page_templates();
    
    // Let's only run on pages for now
    if('page' === get_post_type($post->ID)){
        
        // Loop through and apply
        foreach($templates as $name => $slug){
            
            if($slug === get_page_template_slug($post->ID)){
            
                $post_states[] = $name;
            
            }   
        }
    }
    
    // Return the new list of states, ez!
    return $post_states;
}