Well, there are USB 3 audio interfaces.
There is lots of latency with iPads with some apps. Others not so much. It's unclear what exactly will cure the latency issues. Would this new cpu do it? or would USB 3 help? . Not having controls for buffers and clear latency indicators, doesn't help. Logic and MainStage are very good with this (as are most DAWS).
I'm thinking it's mostly the cpu. Buying a USB 3 Audio interface for an iPad may be a waste of money, considering it's unclear if latency is improved even on a desktop (although bandwidth will improve).
Others will know much more than me, but be careful about erroneous info. But I will say I'm envious of these new iPads as they are extremely powerful, and if there's any latency now, it's going to be the apps fault, most likely.
The example of latency I'm talking about is Amplitube for iPad. I get terrible latency with this. SHAME!

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Developers crap all over the iPad ports of their stuff. Line 6 is probably the worst, then Amplitube. BIAS was never right.
Garageband?
Maybe the problem is cost. Maybe they are afraid to charge $200+, as that is what the big boys will cost.
Something needs to be done.
Frankly, all the effects and guitar stuff is God awful on the iPad for me. Others may love it, being a subjective thing. But the algos are questionable.