Datalink on the CVR? Shades of that familiar old Modem warble eh?
We modified all our CVRs and DFDRs to solid state a while back. Much better results, with an already excellent MTBUR disappearing off the clock. Tape recording quality has never been very good and most mechanical recorder faults were due to either the tape breaking or failure of the tape transport mechanism, in both CVRs and FDRs.
It's certainly a practical proposition to keep a CVR running after a total power failure - there'd be plenty to listen to - but I've long been slightly amused by the regular suggestions that the DFDR should have its own UPS. I'm not sure what useful data it would be recording, with all the ARINC 429 databusses shut down, along with more than 90% of the aircraft systems...