We sure made a big deal about the 2015 Mustang finally making that great leap into the '70s and going IRS, but we all know a live axle still has it's place. That place is the dragstrip, and Ford will provide serious racers with the option.
The solid rear axle will be a bolt-in replacement for the independent rear suspension setup and will initially be available on body-in-white cars designed to be sold to serious racers. Once the live axle suspension kit is available, it's likely to be made available as a kit or an option on the Mustang Cobra Jet, according to MustangsDaily (more details also here).
A live axle is a rugged, cheaper, and generally better option for drag racing or serious Dairy Queen rubber-laying applications, and it's so dman Mustang-traditional it's hard not to be pleased that there will still be an option to get it on the latest Mustang.
Somehow, I think that when the Mustang goes all anti-gravity hovercar sometime in the 2350s, there will still be a live axle option.