I think it would be awesome if it was possible to store calls to a queue when offline like Gamesparks does.
I’m currently working on implementing this for our game myself, with some extra bells and whistles for removing calls in the queue if they’re no longer relevant.
We fake success whenever purchasing items, so making sure the purchase request is sent at some point is good enough. We wouldn’t want to make the player wait or quit if the network’s not available. I think it would be awesome to have some simple official support for this.