Nacnud - Almost everyone I've ever run in to who buys a 24mm T/S lens is buying one for the 24mm full frame angle of view, so I would suggest that sensor does make a difference. Nothing wrong with a 38mm equivalent, but it's not a very practical focal length for the types of images that these lenses are commonly used for. And there are 35mm shift lenses available as well (I own both the Oly and the Zeiss).
As far as the new lenses not being sharp it the corners of a full frame sensor image, that's completely bogus. The Canon 24 II is sharp even wide open into the unshifted corners. It's arguably the sharpest 24mm lens available for any 35mm platform.
Here's the real deal on shifting: Most of the time when shooting buildings, interiors, products, portraits, etc. your shifting is going to be up and down if you're using a horizontal frame, and while there is some falloff in resolution at the extreme horizontal shift on a horizontal frame, there is none visible when shifting up or down. That's not to say you can't shift laterally, you do want to watch the extreme corners though. Is that enough to keep you using a crop sensor? Hell, no. In fact, one of my favorite ways to use these lenses, the 17 t/s in particular, is to shoot three horizontal images that are stitched into a single file that is the equivalent of the 36 x 48 mm frame. Those images, if focused carefully are sharp all the way to the corners, and make for something close to what a 10 or 11 mm lens would see on a full frame, except you've now got the equivalent area of a MFDB. Pretty amazing and even wider than a Rodenstock 23 on an Alpa.
Just to emphasize the point, I'll post an image that illustrates this. These lenses, as I've said before, have changed what's possible. This was actually a handheld image, stitched from three frames - shifted up, down and normal, with the Canon 17. It's the new wing of the Kaiser Hospital in W. L.A. and using a tripod would have brought in the security guards, but you get the idea