Just making an observation / thinking out loud that the requirement to support everything ORDER BY handles / supports (and will handle / support?) might make this function impractical to maintain.
Particularly, does the function really need to support dir => asc | desc | asc nulls first | etc... ? Maybe array_sort() + array_reverse( array_sort() ) will handle most of the practical cases? I don't know.
Composing function calls here seems quite undesirable from a performance standpoint, but maybe I over-estimate the cost of exploding-manipulating-freezing an array datum. Also, while I'm not in a good position to judge the challenge of implementing the sort parameters I would rather have them than not since the order by API has them (plus performance). I also, maybe unreasonably, believe that our extensible type system has already limited the maintenance burden.
