Theoretical discussion here, but ever since the iPad first came out, I've always viewed it as a sheet of glass driven by the software as far as functionality, etc.
Apple's upgrade cycles, as they've always been, are very iterative, in that one generation to the next doesn't necessarily prompt mass upgrades.
So, for a fun topic, hardware wise, what would be a great way for Apple (or any hardware manufacturer) to innovate on the iPad hardware for the next generation?