I cant see the point in the cropping being set in camera. Sure you save some on storage and transfer time, but I can't see that it would be very useful. How often is that going to be the crop you want. I crop almost all my shots a bit. But I bet its hardly ever just the center part of the image at exactly that crop size.
I tend to agree that most of the time, folks who are serious about photography would not choose to crop to an APS-C size when shooting with a full-frame lens because you can always do it in post. It's the same reason that most of us don't shoot JPEG. That said, if you know you're about to shoot something very far away, you have no interest in the foreground, and you are using a shorter lens than would be ideal, there's no reason to waste disk space or speed copying the crap around the edges that you know you won't use anyway. So I could see it being useful in those sorts of situations.
But even that reason is still thinking too narrowly. Imagine a high-pixel-density FF camera with the same pixel density as a crop body. Now imagine that instead of the mirror flipping up, it slides a quarter of an inch up at an angle first, then flips up. With that tiny mechanical change, your full-frame body is suddenly able to use AF-S lenses. When using an AF-S lens, the body would automatically crop.
Such a design would offer enormous benefits to photographers. When I'm traveling, I could bring my 10-22, my 17-85, and my 70-300L, using the latter in APS-C mode for extra reach. When I'm trying to do serious shooting, I could bring my 16-35 L II, my 24-105L, and my 70-300L with a 3x extender. (Yes, these exist. Yes they require manual focusing unless you're in live view mode. Yes, they are freaking awesome.)