I wouldn't be surprised at all if sometime over the next 5 years, there's a Lightning/USB 3 cable. Or a Lightning/Thunderbolt cable. And you'll be able to plug that cable into whatever 2012 generation iDevice you like. But you'll still get less than USB 2 speeds. Because the device itself is the bottleneck. USB 2 can handle 480 Mb/sec, or around 30 MB/sec in real life. And most likely the flash memory and interface controllers can't handle anything faster.
I'm sure the geniuses at Apple could have out a fancy blue USB 3 end on the current Lightning cable. But then everyone would be bitching that their phone was only transferring data at USB 2 speeds.
Clint