Example of how to implement separate customizable templates for plugins (similar to how eg. WooCommerce uses them)

template-loader.php

$template_name = 'my_template.php';
$load_template = plugin_dir_path(__FILE__) . 'templates/' . $template_name;

/**
 * See @link http://codex.wordpress.org/Function_Reference/wp_upload_dir#Usage
 */

if( file_exists( $upload_dir['basedir'] . '/my_plugin_name/' . $template_name ) ) { 
	$load_template = $upload_dir['basedir'] . '/my_plugin_name/' . $template_name;
} else {
	/**
	 * See @link http://codex.wordpress.org/Function_Reference/load_template#Examples
	 */

	if ( $overridden_template = locate_template( 'some-template.php' ) ) {
		// locate_template() returns path to file
		// if either the child theme or the parent theme have overridden the template
		//load_template( $overridden_template );
		$load_template = $overridden_template;
	}
}

// avoid instant explosions
if( !empty( $load_template) ) {
	load_template( $load_template );
}