MIDI over Bluetooth on iOS would be a breakthrough in convenience, portability, as well as save you some money. MIDI controllers with Bluetooth built in would be wireless (obviously) providing for more portability, as there would be no need for an interface or cables. If there was a keyboard like the nanoKEY2 that supported Bluetooth, your mobile studio could be expanded with a physical instrument that you could take with you on those hour long train rides to work. Also, there would be no need for a WiFi network, and your dock connector would be freed up for an audio interface.
Another thought: A free app
could (has been – App Store link) be developed that sends MIDI received via Bluetooth to another app via Virtual MIDI instead of waiting for every developer to add Bluetooth support. Similarly, a physical Bluetooth MIDI plug could allow you to use the hardware you already own.