For a start you can't run Cubase 6.5 on an iPad, and don't forget you would need all of the same 3rd party plug-ins on your playback device as well as Cubase itself. This would include virtual instruments and, potentially, your entire sample library. You could freeze instruments and tracks, but then it would be easier and quicker to just render a mix.
Then you would need to port all of the Cubase data from device to device. I don't know about you, but some projects I'm working on can be over 5GB for one song.
I can't see much going for this idea. It's far simpler to render a mix on your recording/mix computer and play that on your other devices.
Networking your computers/laptops/pads can help enormously. If I wanted to listen to a vocal solo-ed on my living room hi-fi system I would simply sit in the living room with my laptop, navigate to the project folder on my studio PC from my laptop (audio output plugged into my hi-fi) and play it from there.
An Eagle for an Emperor, A Kestrel for a Knave.