This is meant to be kind of like the 'Utility bike products you wish existed' thread, except more specific to Xtracycles.
For myself, the number one would be some kind of steel mesh I could pull over my Freeloaders when they have bags in them, something I could lock down; essentially a PacSafe for the Freeloaders. This would make it easy to hit multiple grocery errands, because I can almost always park my bike publicly when I go shopping, so anything that requires tools to tamper with will almost certainly be left alone. Some integrated pouch for storage when not in use would be great also.
Everyone wants a center stand, but Xtracycle is going to make us one if we're patient! Anything else you find yourself craving as you cycle about, without a care in the world, hauling more than seems possible and making it look easy?