It would be really nice if convex had the ability to do an array-contains query at the database level. Firestore has this(https://firebase.google.com/docs/firestore/query-data/queries#array_membership) and you could do some very powerful filtering by putting a bunch of identifiers in an array, and then doing an array contains query to find documents where that array contained one of those identifiers.
Other prior art: https://github.com/cockroachdb/cockroach/blob/master/docs/RFCS/20171020invertedindexes.md