For me, the 1.3X crop on a FF sensor is a gimmick. By switching from FF to 1.3X crop will not by us anything except a smaller file size and a narrower angle of view. We can do the same thing at post process by cropping the FF picture.
Absolutely. 1.3x crop mode is pointless. 1.6x crop mode (assuming to afford EF-S compatibility) is impossible.
For Nikon it makes a little more sense, because their crop lenses vary only in image circle cast; afaik the physical specifications of the mount are identical. With EF-S, lenses are allowed to intrude into the mirror box by a specified amount, and lenses that do (generally wide angle) will not clear a FF mirror.