If you're looking at "any and all" cargo solutions, it's worth considering Carradice's SQR ("Seatpost Quick Release") series of seatpost-mounted bags; there's the Tour, Slim, and Trax, which are all 16 liter bags of varying dimensions, and the Glentress 5 liter waterproof bag (which is what I have), as well as the SQR System, which basically gets you mounting hardware and a frame to which you can attach most any bag (or what have you). Capacity is 10kg (22 pounds), nearly that of the CrossRack, and much more than any other seatpost mount I could find (and the mounting is very secure and hardware is very high quality).

Yes, these are all seatpost mount, like Xootr's CrossRack, but the SQR mount is pretty low profile, and can be mounted right under the seat, so the seatpost can still go down almost as far when you fold (end of standard length seatpost gets within about 2-1/2" of the rear wheel.

(BTW, if you or anyone else do end up going with Carradice SQR, be sure to select "Size: large", which gets you mounting rings that will fit around the Swift's 34mm seatpost -- the "Size: standard" rings are too small.)