There is already a threadt about a DJ version of Spotify which is marked as IMPLEMENTED. But in my opinion it is not. There is no way of running iPad apps anywhere but on an iPad which I don't have. So I can't use it. Why don't you add a DJ interface to the PC client? Or let people choose between two clients, one with the DJ function and one without. If that's not possible (I wouldn't know why), an Android app would help many people, even if they don't own Android devices. It's possible to run Android apps on Windows using BlueStacks or the official Android SDK emulator.
Anyway, why did you choose the iPad as the platform for the App, not Android or PC?
Ah, and a Linux (Ubuntu in my case) version would be awesome!!!! The missing DJ interface is the only reason why I didn't get Spotify Premium for a long time and may be the reason why I'll go away again.
PS: Please don't mark this as duplicate idea, I think it isn't