Looking at the Infocom games, I can name several titles which use ship directions. So, it’s not a case of a feature needed by very few games. Boats, ships and spaceships are rather common in text adventures.
Also, this was a lot easier to implement in a performant way if we made it part of the library. And if you don’t define OPTIONAL_SHIP_DIRECTIONS, it changes absolutely nothing - the code compiled by the library is identical to what it was before ship directions were included. An extension would have introduced more overhead when included too, or made the library more complex because you’d have to be able to replace the Directions object entirely.
We’re also aiming at adding the option of completely custom directions. I’ve seen a few games that use left, right etc, and we could accomodate that.