Extending Elementor Elements

I'm trying to create a custom "column-like" element that can house child content, but after extending the `Elementor\Element_Base` and registering with the element manager, the element is still not showing up in the editor panel. I'm starting to get the feeling that elements weren't designed to be extended, but this is a feature that would prove extremely useful, especially if it were as easy as creating new widgets.

```php
// Registering in add_action( 'elementor/elements/elements_registered', ... );
Elementor\Plugin::$instance->elements_manager->register_element_type(new Elementor\Element_Custom());
```

I have been looking for the setting/piece of code that causes the column element to show up in the editor panel but not the section element with no luck.