I can get the transfers between friends part, but why between platforms? That makes zero sense from a business standpoint.
The only way that would work is to have game companies manufacture and distribute an external storage medium themselves, because platforms sure as hell won’t say “Oh you bought a license on another store? Sure, you can use our CDN for free!”. And now we’ve almost reinvented game CDs.
Game mechanics can be patented. It’s stupid, but things such as “loading screen mini games” and “overhead arrows pointing to your objective” have been patented. The second I believe even got enforced once.
I think these kind of things have been getting approved less and less, but I wouldn’t be surprised if “balls that contain monsters” was patented back in the early days too.