You're suggesting a [d] choice, subdividing the horizontal headers. It seems to me like a pretty radical change, multiplying the number of columns, and it has also the potential to give poor results visually. Let's see if more feedback comes.
yes, I know, plan @d needs lot of new code - and described feature is from "nice to have" kind.
The prerequisite is enhancing drawing system in psql to support multiattribute (records) cells - what can be nice feature generally.