After the recent article about the state of the Unity Editor's porting to Linux, the Unity team has put out a more concise post on the company's official blog.

Details are largely the same as in the previous post that it will support 64-bit Linux and will be officially supported on Ubuntu going back to as far as 12.04 LTS. The forthcoming Unity Linux Editor should be able to export to all of the same platforms as the OS X editor, with the exception of iOS.

From this post though it doesn't sound like it will work with the open-source Linux graphics drivers but "will require modern, vendor-provided graphics drivers"

More details via the blog post at Unity3D.com.