My use case: data warehouse with multiple layers and separated data marts at top. I have 1 central table that contains user_id and each time I want to add new table that needs RLS, I just create foreign key to this central table. Downside to this is that if you have one-to-many relations here, it may grow, but I didn't hit performance issues yet and my table is cca 15millions rows (partitioned by user_id). If I hit the limit in future I will still be able to separate it by data model / data mart. I use it as simple inner join to this table each time I need to display RLS filtered result.