This is a pretty substantial request, but I'm just throwing it out there.
For games that don't have multiplayer components but want to utilize some cloud logic, some form of SDK-facilitated client-side caching would be amazing. For example, casual single-player games like endless runners may be played in areas without cell phone signal (airplanes, for instance). In my game, I am manually writing encrypted JSON versions of loot table, player progress data, etc. to the Application Support directory each time the call to the online component is made. The game logic ONLY reads from these client-side repositories, which are consistently overwritten by the versions pulled from GS, and cloud code validates any changes made.
If a method were implemented in the SDK to ease this process and allow developers to quickly "opt-in" to client-side caching of certain data sets (especially metadata collections), I believe it would increase adoption of GameSparks for all kinds of games by enabling a greater degree of offline freedom.
If GameSparks already has this capability and I've missed it...well I'm embarrassed and have wasted a lot of time, haha.
Thanks for the suggestion, it's something we may consider down the road. Durable requests may be of some use to you here, you can read about them here. Requests set as durable will be queued by the SDK until it can be sent which is useful for games that may have periods of being offline.