Can you add methods to node-entities? What is the preferred way to add functionality to nodes? 
More explicitly stated: What is the node-entity equivalent of the Entity-class from the entity-API-module?

Sometimes you want to add methods to a entity. That is possible when using the entity-module, where each entity has a "entity class" property. You can take this entity class and extend it to your heart's content. 

However, this is not possible with node-entities, since these don't use the "entity class" attribute. 

So, the following code would work if drupal-core worked like the entity-module, but throws an error as is: 

function myNode_entity_info_alter(&amp;$info){
    $info['node']['entity class'] = 'MyNode';
}

class MyNode extends Entity{
    public function sayHi(){
        drupal_set_message("Hi!");
    }
}


function myNode_entity_load($entities, $type){
    if($type == 'node'){
        foreach ($entities as $entity) {
            $entity-&gt;sayHi(); # Error: Call to undefined method stdClass::sayHi()
        }
    }
}


How can I make this work with node-entities?

PS: as a follow-up question: is this any easier using drupal8?
I believe I have found something that does what I want: https://www.deeson.co.uk/labs/extending-entitydrupalwrapper

The basic idea is that, since drupal-core doesn't facilitate the extension of entity-classes, we use the entity-metadata-wrapper instead. 

The above example would then be reformulated as such: 

class MyNodeWrapper extends EntityDrupalWrapper{
    public function __construct($data) {
        parent::__construct('node', $data);
    }

    public function sayHi(){
        drupal_set_message("Hi!");
    }
}

function myNode_entity_load($entities, $type){
    if($type == 'node'){
        foreach ($entities as $entity) {
            $emw = new MyNodeWrapper($entity);
            $emw -&gt;sayHi();
        }
    }
}


This appears to be a very reasonable approach. Only thing I dislike about it is that you can't use entity_metadata_wrapper to get the MyNodeWrapper-wrapper.