I like the concept. The rubber would probably need to be replaced when sent back in but it seems like an easy replacement. You have to clean it out well to ensure there is no contamination. Unlike an ink cartridge, a user can easily accidentally or purposefully contaminate the cartridge/resin.
I would even appreciate FL selling resin in bulk containers (gallon of resin, like boxed wine) so you can refill a slightly more robust cartridge yourself. Throwing away a plastic bag for every 1 gallon of resin and recycling the outer cardboard is much better than throwing away these cartridges every liter. You could also cure the resin residue inside a clear plastic bag.
FL will be launching their “Long Term” resin tank soon so I am sure they are working on reducing cartridge waste also.