Functions For Calling Specific Elements

It sounds like get_template_part() would do the trick.

In element.php you could simply call get_template_part( 'element-item' );, which would then include the element-item.php file from your theme.

You could wrap this up in a function if you wanted to, e.g. get_element().

function get_element() {
    get_template_part( 'element-item' );
}

This approach would allow you to add logic into the get_element() function so that it only gets the template part under certain conditions and it would keep the element.php template from our example cleaner since the logic would be bundled up in get_element().