I proprose to link collections together to display related movies/collections. If we add a related collection for a collection, we can see and edit the relation in both collections.
A manual feature of related collections for a first implementation will be already a good one ! An automatic feature would be wonderfull (but more complicated to do).
Here an example of the expected feature:
An other solution is to display only the name/image of the related collections (I think this is more easier to implement and more readable for the users):
