I just read through the code, looks really good. The example shows post<->post, but I would imagine it could be applied to any custom type (being that they all “inherit” from post anyway, in that strange lovely way WP does things).
One follow up question – with different types (like Movie + Genre), would you add the Relationship ACF to both the movie and the genre for the above snippet to work correctly?
As a sidenote, and in hindsight, I realise genre is really a poor example (ie could be taxonomy, but just an example 🙂 )
