The frame I've got is steel and not going to win any awards for being lightweight - given how hilly Lancaster is, it would be good to keep the weight down on the platform where possible.
The wheels will be easy enough to remove, and if the box is removable too, then that's fine storage-wise. No need to get any more foldy than that, and I don't think that would be possible anyway without serious frame re-workings.
The box will be useful for food shopping and maybe participatory workshop scenarios. I wouldn't be surprised if it has to carry a sewing machine at some point, and loads of random metal and wood (nice work with the clamps, Kim!) are all par for the course.
Additional chassis crossbars would be a good move, I think, but welding access is still unlikely. Probably they're retrofittable to a certain extent, or it might be possible to bolt something on.
I'm trying to remind myself that a) in its original form there was just a thin layer of cloth supporting a couple of small children and b) wood can always be replaced if necessary.
Thought: I suppose I'm going to have to contrive to make it D-lockable as well.