There is a way to compress a WUD into a WUX which makes it closer to the games actual size while maintaing a single file structure which would make booting much much faster.
At the moment Loadiine cannot boot the format, so its kind of useless, but maybe oneday we will all be using WUX files to play our backups. Like the CSO on the PSP
But getting files back into WUD or even the installation files is not possible.