Switching apps with midi, would be a key feature to streamline using the ipad as a keyboard, with a midi controller. Having a bunch of synths loaded up in audiobus, each on their own midi channel, and just switch channels on the keyboard to change your sound. The app switching with midi would mean you'd be able to hit a button on the keyboard, and be able to edit your synth sound on the ipad.
Some midi keyboards have the ability to fire a midi program change message, at the same time that you switch presets on the keyboard, so you could set it up to switch midi channel to a different synth on the ipad, and switch the app on the ipad screen at the same time. Slick!
AUM + Midiflow until Mainstage come to iOS...
I use the akai mpk249. You can program any button to send keyboard commands such as command + tab. It’s very useful for switching between apps or going to the launcher page.