> ...So we'd want the same index usage as > =ANY(array) but would like faster row checking than we get with an array > when other indexes are used.
We kinda already do this since PG14 (commit 50e17ad281), actually. If the list is long enough (9 values or more), we'll build a hash table during query execution. So pretty much exactly what you're asking for.
Ha! That is great. Unfortunately we can't rely on it as we have customers using versions back to 12. But good to know that it's available when we bump the required versions.