Entity Reference of multiple types
While relation can handle multiple entity types in a single relation type it can't reference Views. It's a challenging problem for two reasons: the view_id is a string unlike say nid so a database schema made to refer numeric IDs won't be able to copy with views. Also, views is not stored in the database necessarily so the utility of such reference is limited.

It should be possible to maintain an entity in the database that has a numeric ID and all it contains is the Views ID. Your only problem becomes when someone changes the machine of a view that is maintained in code -- how do you plan to be notified of such a thing when it happens outside of Drupal?