I've read the user manual and FAQ on ports for the new 2015 Retina MacBook and can't tell if it supports target disk mode.
Apple's article on target disk explicitly says Firewire and Thunderbolt are required for target disk mode but the excellent iMore review article says:
You can transfer data at up to 5 Gpbs over USB 3.1, USB 3, or USB 2, or over ethernet with a USB adapter. (Including target disk mode.)
For the purposes of this question – target disk mode is exposing the internal MacBook storage using firmware and not the OS X installed on the computer itself.
What is needed to place this Mac in target disk mode and connect it to another computer that would presumably see it as a USB 3.1 Gen 1 hard drive?
Best Answer
Yes - you need an USB C data cable to use this and the power cable Apple ships isn't a data cable for these needs, but the firmware and hardware support target move over USB.
Apple's MacBook ports article now has a section titled "USB Target Disk Mode":
Since this section was still available two days ago, and the MacBook launched on April 10, 2015 — I would say the answer is almost certainly yes, but not with the cable it comes with.