Don't be so sure. The iPad probably has more CPU horsepower than the last generation of keyboard you were using.
It's things like this that perhaps get our hopes set too high. It's somewhat unlikely that the iPad has enough horsepower to generate 128 voices with multiple high quality effects with NO dropouts, run a sequencer and do a full arranger mode and run a live vocal transposer. Maybe in ten years...
But I'll tell you what... If anyone can take the open concept to fruition, Apple have deep enough pockets to do it! Trouble is, all the current players are also-rans, who can't afford to create the integrated soundsets and styles that we expect from a TOTL closed arranger. Maybe Apple can afford to take a swing at it..?
Many modern VSTi's can bring even a decent tower or hot laptop to its' knees, and only get a few notes of polyphony from it. Be quite a while before the iPad has enough juice to go the distance.
The best leveraging of a thing like the iPad is to stick completely to MIDI. I would not be surprised if this has enough juice to run a soft arranger and a Karma module at the same time, as long as it wasn't being asked to generate the sounds, too. Hook it to an existing WS, it could be VERY powerful. But It's going to be a while before this thing as a standalone unit is going to be any better than what we can currently get out of a decent laptop, and nobody has shown me to my satisfaction even one of THOSE being a decent alternative to a hardware arranger...