I would also like to give my vote for prioritising midi controls for the app. I am a recent owner of Cubasis 3, but since this is already an extensive thread on the issue, I thought it better to write here.
It is very cumbersome to have to start recording, mute tracks, adjust volumes etc with the touchscreen, when all these controls are easily accessible from my midi controller. Even though I have the 12.9 inch iPad, screen real estate is still very valuable, when using DAWs and midi control would allow the mixer to be closed and I could still easily adjust volumes while having the maximum screen space for tracks.
Other then that, I think it is a very nice DAW for the iPad, but this basic functionality included in almost all other music production apps I own, is really bringing the experience down as a whole.