You could use it as the logic board for a micro drone, something the size of a dime perhaps. Or other applications where weight or space are extremely limited. Another example might be a medical implant of some sort, this is small enough that it could be a part of a device that is meant to be placed inside an artery, or an eyeball, or an ear canal.
I make specialty vehicle electronics. My immediate thought was very small and cheap sensors. Similar to tire pressure monitoring but wired with CAN or something similar.