In addition to term-based queries, we currently support prefix, regex, and wildcard queries on certain metadata fields like _ignored and _routing. It’s not clear that supporting these additional query types is useful, and it limits how we’re able to store these fields. As an example, _id fields do not support these queries, and we’re able to encode them using a flexible scheme.

Unless they're actively used, we should consider deprecating + eventually removing support for these query types.

Relates to #34089, where the discussion first arose.