Aside from the other features it is clear people just do not upgrade iPads like they do iPhones, so they will either have to gimp the device(s) and increase iOS requirements and miss features, or embrace it and throw down the gauntlet with Storage. This would align with the rhetoric of Tim Cook stating the Services category being key long term, they are aiming for people consuming more via services - to do this you need either cheap data plans or local storage.
iPad/iPad Mini Storage sizes: 64GB, 128GB, 256GB. Increase the base price in the UK to £449, £549, £649. Then the usual +£100 for cellular.
I'd also like to see the iPad Pro updated similar to the iPad 4 saw (Introduction of a higher capacity model in the Feb following a release the previous October), storage options of 128GB, 256GB and 512GB, at price points £679, £799, £899.
The above pricing would give the iPad Pro a premium over the Air of £130, (comparing 128GB vs 128GB) which would be 'fair' for a larger device and hopefully stop people comparing the 16GB Air 2 price to the 128GB iPad Pro price, which is ridiculous.