Comment "Simple" solution (Score 1) 491
The solution to this would be to add a new command to the ATA spec, call it FREEZE or something. If a drive receives this command, it won't do any writing/erasing, neither on its own or in response to ATA commands. Then you just create write blockers that also send this command.
Of course, this both requires new drives and new write blocker hardware, so it probably won't be implemented.