There is no SACD hard drive based solution I am aware of. I think that is because the SACD format is proprietary and uses encryption that prevents the files from being created from the discs.
In my view there is not much indication that anything other than regular old redbook CD will be the standard anytime soon. At this point in time, if you want to be at the cutting edge, I think the key is asynchronous USB. You use the computer as a transport and feed a DAC via a specialized mode of USB.
Everything you need to know is here
http://www.ayre.com/pdf/Ayre_USB_DAC_White_Paper.pdf
In my view there is not much indication that anything other than regular old redbook CD will be the standard anytime soon. At this point in time, if you want to be at the cutting edge, I think the key is asynchronous USB. You use the computer as a transport and feed a DAC via a specialized mode of USB.
Everything you need to know is here
http://www.ayre.com/pdf/Ayre_USB_DAC_White_Paper.pdf