Ah I see. I didn't really understand the requirement. That would indeed be a nice one though pretty hard to configure for general search because the results can come from so many sources.
As well as that, for special-purpose things like movies it does in fact have a ranking for those by querying common sites like IMDB directly as an engine. So in that case you can use the weighting system to show preference. It doesn't seem to support letterboxd as a source but it does some others: