Yes, this is going to be a killer feature!
Building Core MIDI right into iOS was a great move by Apple, and this looks like such a better alternative to the Line 6 MIDI Mobilizer device and/or the DSMIDI wi-fi solution.
I already use the Camera Connection Kit to plug in a USB condenser microphone (the BLUE Yeti) to the iPad for multitrack recording and it works great.
There are loads of great synth and sequencer apps already in existence that could benefit from this capability, with more to surely come, and I for one can't wait!