Better support for case-insensitive text?

A persistent user on Reddit recently asked about support for case insensitive text: https://www.reddit.com/r/haskell/comments/7erfio/persistmarshalerror_when_using_text_haskell_value/

Postgres has it's own citext type, and I came up with this code to use it: https://gist.github.com/MaxGabriel/9e757f2da60ac53b45bb06b2b097d86b

The core of which is these instances:

instance PersistField (CI Text) where
  toPersistValue ciText = PersistDbSpecific $ TE.encodeUtf8 (CI.original ciText)
  fromPersistValue (PersistDbSpecific bs) = Right $ CI.mk (TE.decodeUtf8 bs)
  fromPersistValue x = Left $ T.pack $ "Expected PersistDbSpecific, received: " ++ show x

instance PersistFieldSql (CI Text) where
  sqlType _ = SqlOther "citext"

instance (ToJSON (CI Text)) where
  toJSON a = J.String (CI.original a)

instance (FromJSON (CI Text)) where
  parseJSON (J.String text) = pure $ CI.mk text
  parseJSON v          = fail $ "Expected String, encountered " ++ (show v)

Any thoughts on if this is the best approach, and if the code should be incorporated into Persistent proper? I would say definitely not for the aeson instances. And only possibly for the PersistFieldSql instances, since they'd be orphans and only right for persistent-postgresql (for MySQL and SQLite, you would want to use a normal string type with a case insensitive collation (this is actually the default for MySQL)).

My instinct is that the best option would be some new package with extra instances for all the different Postgres types (I know of the geography types and citext; I'm sure they're more), which may or may not be part of persistent's repo. Anyone know if such a package already exists?

cc @parsonsmatt

Start with the linked gist and the issue's discussion of PostgreSQL's citext type and PersistField instances. Compare the proposed PostgreSQL approach with the stated MySQL and SQLite differences. Done requires an agreed scope for Persistent support or a separate package, but the issue does not specify files, tests, or a concrete implementation.