This is awesome for me, and one of the areas that iOS absolutely kills Android.
Android still has a long way to go before it can offer anything like iOS for music creation, but this is a big step in the right direction.
I made a quick and rough video to show it working.
If you have a USB controller that is bus powered, then you can play your keyboard anywhere!
We just need more apps that support this feature now. I only know of one (the Grand Piano app I use in the video).
If anyone knows of any others, please let me know.
PS - I wasn't sure if this belongs in General, Accessories or Apps, so if it's in the wrong place, please move it.