Half the price of a Mac mini
Absent the need for the fastest possible I/O, a headless Mac mini sounds like a more convenient "docking" option gigabit when you need the speed, wireless when you don't. Plus, the mini can be used for Time Machine. Plus, the mini can be used as a media server. Plus, the mini can be used as an AirPlay speaker server. Plus, the mini can be used for Batch rendering, audio/video encoding, and similar processing tasks. Plus, the mini is a whole frickin' backup _computer_. Gigabit isn't 10 gigabit, but neither is FireWire 800 or USB 2, and you hardly need this unit for DisplayPort and/or Thunderbolt merely, so the applications for this thing seem rather limited.
Sure the price will come down, but plug the bill of materials for what amounts to the better part of the I/O subsystem of a laptop into the usual "******* crazy retail accessory markup" formula, this is probably just what you get. Why can I buy a _device_ bundled with a USB A-B cable for the retail price of a USB extension cable? Because said device never comes with an extension cable. And if they sold it for less, they'd make less money, yet the too-short cable bundled with your new device wouldn't suddenly grow longer. This is just the 21st century's version of batteries that cost more than toys.
What's really needed is a $600 Beats by Dr. Dre Thunderbolt dock with gold-plated connectors and a special headphone jack for heart-pumping bass...