A print server would be a good idea. I see some commercial routers with a built-in USB port for a printer connection. I am sure there are a lot of Monowall users who use generic standard PCs that have at least a few USB ports on them. It would be nice to use them.
I think this is not at all in the philosphy of m0n0. I am not a developper, but I think using USB driver, maintain this with the evolution of hardware (a lot of chip are released every year) would result in a bigger m0n0 image, slower boot time and more ressources utilisation...