I have to ask, though .... In mission-critical applications, are many organizations really using HDD for long term offline storage? I'm thinking tape is still king for things like corporate backups, archiving and similar applications.
Eventually, once flash memory becomes cheap enough, hard drives will vanish. There will just be very little reason for them to exist. It certainly won't be for mass storage applications. There's virtually no way that HDDs will increase in data density as quickly as flash. Indeed, with 16TB 2.5" SSDs available today, SSDs have already surpassed mechanical drives in storage density per unit volume.