register-template.php

<?php
/**
 * Plugin Name: (WCM) Backbone/Underscore template loader
 * Description: Loads Underscore (or other) templates using the WP Dependency API
 */

/**
 * @author Franz Josef Kaiser http://unserkaiser.com/
 * @link http://chat.stackexchange.com/transcript/message/19439060#19439060
 */

// Allows registering Backbone templates as scripts
// Add type="text/template" and id="{handle}" for Backbones .tmpl <script>s
add_filter( 'script_loader_tag', function( $html, $handle, $src )
{
	if (
		empty( $src )
		or ! strstr( $src, '.tmpl' )
	)
		return $html;

	$dom = new \DOMDocument;
	$dom->loadHTML( $html );

	/** @var \DOMElement $tag */
	foreach ( $dom->getElementsByTagName( 'script' ) as $tag )
	{
		if ( $tag->hasAttribute( 'type' ) )
		{
			$tag->setAttribute( 'type', 'text/template' );
			$tag->setAttribute( 'id', $handle );
			$tag->appendChild( $dom->createTextNode( file_get_contents( $src ) ) );
			# new node: 25% faster than
			# @link http://chat.stackexchange.com/transcript/message/19567599#19567599 
			//$tag->nodeValue = esc_html( file_get_contents( $src ) );
			$tag->removeAttribute( 'src' );
			$html = $dom->saveHTML( $tag );
		}
	}

	return $html;
}, 10, 3 );

use-case.php

<?php
/** Plugin Name: Underscore Template Test */

add_action( 'admin_enqueue_scripts', function( $screen )
{
	if ( ! in_array( $screen, [ 'profile.php', 'user-edit.php', ] ) )
		return;

	$ext = (
		! defined( 'SCRIPT_DEBUG' )
		xor ( defined( 'SCRIPT_DEBUG' ) and ! SCRIPT_DEBUG )
		&& ( defined( 'COMPRESS_SCRIPTS' ) and COMPRESS_SCRIPTS )
	)
		? '.min' : '';

	$url  = plugin_dir_url( __FILE__ ).'assets/';
	$path = plugin_dir_path( __FILE__ ).'assets/';
	$deps = (
		defined( 'CONCATENATE_SCRIPTS' )
		and CONCATENATE_SCRIPTS
	)
		? [ 'main', ]
		: [ 'controller', 'models', 'views' ];

	// Load template
	// Currently without {$ext}
	// Use HTMLMinify to compress your templates
	wp_enqueue_script(
		'template',
		"{$url}/templates/template.tmpl",
		$deps,
		filemtime( "{$path}/templates/template.tmpl" ),
		true
	);

	// Load main, concatenated file or single files
	if (
		defined( 'CONCATENATE_SCRIPTS' )
		and CONCATENATE_SCRIPTS
		)
	{
		wp_enqueue_script(
			'main',
			"{$url}/main{$ext}.js",
			[ 'underscore', 'backbone', 'jquery', ],
			filemtime( "{$path}/main{$ext}.js" ),
			true
		);
	}
	else
	{
		wp_enqueue_script(
			'models',
			"{$url}/models.js",
			[ 'underscore', 'backbone', 'jquery', ],
			filemtime( "{$path}/models{$ext}.js" ),
			true
		);
		wp_enqueue_script(
			'views',
			"{$url}/views.js",
			[ 'underscore', 'backbone', 'jquery', 'models', ],
			filemtime( "{$path}/views{$ext}.js" ),
			true
		);
		wp_enqueue_script(
			'controller',
			"{$url}/controller.js",
			[ 'underscore', 'backbone', 'jquery', 'models', 'views', ],
			filemtime( "{$path}/controller{$ext}.js" ),
			true
		);
	}
} );