That module was created a long time ago. SilverStripe will now automatically include vendor/autoload.php if it exists, so that module shouldn’t be required any more.
g4b0, we’re planning on making core code PSR-4 compliant and loading it with composer’s autoloader - not writing our own PSR-4 autoloader. Because we’re including vendor/autoload.php (as mentioned above), SilverStripe will already autoload any code that’s registered with composer’s autoloader.
As Marcus said, you don’t need to create a module just to take advantage of this - any PSR-4 or PSR-0 compliant packages that you add to your main project’s composer.json will be autoloaded automatically. For example, if you add "ezyang/htmlpurifier": "*" to your project’s requirements and run a composer update, it will be autoloaded.
tldr; we already support this :)