In https://github.com/magento/magento2/blob/master/app/code/core/Mage/Catalog/Helper/Output.php there is an interesting logic that allows to specify callbacks for processing attributes.
But I feel, that the same purpose can be already served by simple events.
When not adding events like "catalog_helper_output_productAttribute" and "catalog_helper_output_categoryAttribute" which serve as hooks for the events processing ?