Understanding that what is suggested is a non-survivable recording, and given that 12 hours of CD quality audio will fit on about 12GB, would the solution be recording onto an SD card in some non-rugged outboard of the CVR system, with the SD card being the property of the captain, to be removed at the end of the flight unless there's a need of the recording?
All that is not that easy.
You cannot just put consumer HW into a unit like that. There are far higher requirements with regards to reliability (temperature, high altitude radiation ...)
Furthermore: after 1-2 years consumer chips will no longer be manufactured. So the whole process would need to be started again. The certification surely costs > 100.000 USD and takes many months. That can't be done all the time. Therefore HW like that relies on special industrial chips that are made for a long period of time. Those chips are not developed like consumer HW.