From what I understand, the right and left hulls are made symmetric as they each come out of the same mold. I guess it reduces the complexity of manufacturing and means they only have to create/stock one "part". So those unused threaded inserts (the port ones on the port hull and the starboard ones on the starboard hull) are the unused mates of the ones mounted on the inside that are available for the jib cleat option.
I use mine to mount pretty effective oar locks. Earlier thread:
https://www.hobie.com/forums/viewtopic.php?f=123&t=58726