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.
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.
How would you ever actually practically use this
Same way you would in any other microcontroller application, but smaller, so the whole device can be smaller.
Get small enough and we can really have those bloodstream robots.
Maybe an actual useful smart ring?
In small things. Probably not very feasible for hobby projects unless you can get it soldered on when the PCB is built.
BGA, like in the photo, isn’t the only option. There are options only slightly larger with hand-solderable packages (if you’re good at soldering)
This is already technically hand solderable with the right equipment.
In any use where size and or weight is important. For example wearables and flying drones
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.
fly-sized spy drone
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.
Wrist watch.
see comment from @Lumberjacked (it is complicated !)