I think the primary use of a DAW on a portable device such as the iPad will depend on the way developers see these devices. Luckily, it looks like devs start understanding that an iPad for example has all it takes to be regarded a very reasonable semi professional base rig for serious “on-the-road” production. This is also helped by very high-class outboard equipment like iOS products built by Apogee, and more and more of them are coming. As soon as IK Multimedia support Audiobus, Cubasis will be able to replace my entire desktop rig up to the point when it comes to mastering which I have always done using Wavelab and two sets of decent speakers.