I'm really not sure why crl doesn't have the ellipse marquee start growing from center instead of corner. It does this with the circle polygon tool, why not this selection tool? Also, I would like to do crl + shift in order to both expand from center and to lock it to circular.
Same thing applies to the rectangle marquee. Same thing also applies to the crop tool, which (in unconstrained mode) is missing both shift and crl.