Get posts with no relationship

Hey, I'm making a suggestion here instead of a new post.

It seems like there's no way to query for objects that simply have a relationship ID.

It would be great if the 'relationship' query argument could accept EXISTS or NOT EXISTS. Similar to meta_query. Instead of passing it via "to" or "from" maybe introduce the "compare" param?

So for a modified example based on the documentation, something like this:

$query = new WP_Query( [
    'relationship' => [
        [
            'id'   => 'events_to_bands',
            'compare' => "EXISTS"
        ],
    ],
] );

If this is not feasible, is there already a way to query all objects with a particular relationship?

Now I'm using Relationships to "feature" a post in a category (which they are, separately, also categorized in).

But if I can't query all related (featured) posts, I will have to use a field like "taxonomy_advanced" field which is less ideal for my case.

Thanks!

I thought "exists" and "not exists" were not very different. But sure, I'll make another topic.

Using advanced taxonomy is possible but misses out on the advantages of Relationships, like performance and being able to view the connection from both sides.