I'm wondering how difficult it would be to build OpenWrt for this particular device. They're rather cheap and have okay specs (128MB of RAM, 1TB HDD, USB).
I saw another thread for this device, but looks like it died out years ago.
It is possible to run debian on the device as can be seen on the doozan forum.
Running OpenWrt is possible but will require some development & testing. The nas only has a very small flash chip for u-boot and the rest of the firmware lives on the internal sata drive. It is possible to run OpenWrt from the sata drive since the same method is used for the WD MyBook Live. However none of the current kirkwood devices use this method at the moment.