...when the manufacturers of motherboards, Hard drives and many other peripherals stop using legacy technology. Motherboards that have a number of USB2 & 1394 connectors in place of ATA interfaces, parallel &serial ports etc. It would take several manufacturers to switch simultaneously for anything to really happen.

Wouldn't a 1394 or USB2 based HD be more efficient in controller circuitry anyway? No buffering from parallel to serial to handle.
Drives would be truly hot swapable.
Imagine a RAID array connected via 1394b to the host, each drive has its own 1394 cable to the controller.

Just a thought.