I doubt there is much technically in the way other than it being of fairly limited use in most cases. Your iPod case has a ~0.5Ah battery while an iPhone 14 Pro Max has a 4.3Ah battery. Add in the inefficiency of wireless charging and you would be lucky to get a 10% charge off the iPod case.

IIRC, some Samsung devices have the capability of charging between devices, but I personally can't imagine anyone I know using this. Perhaps to charge an Apple watch wirelessly from the phone while the phone is plugged would be useful when traveling.