Thanks all for helpful responses so far.
So it is possible to put a Brompton under the cart, but not with Dahon... I may do a bit research on shopping cart sizes: which local market has the biggest cart?
In terms of panniers, did anyone try Sunlite toploader and grocery getter? Some toploaders seem to have padded and insulated walls, ideal to carry a digicam and a sushi lunch for weekend cycling, while grocery getter seems big enough to hold a bagful of grocery. Both are mounted on the rear rack, and I'm not certain if they can mount nicely on Vitesse.
Rafael, can you expand on what kind of problems you experienced with rear panniers?