I have confirmed that 30-Bit color is working on a 27-inch iMac. A 16-Bit greyscale ramp was used to test. Applications which support this capability are quite sparse. At the time of my testing Preview worked and Pixelmator did not. It is likely that applications need to optin to use this feature. The standard 24-Bit pipeline is indicated with Pixel Depth: 32-Bit Color (ARGB8888). New 30-Bit color pipelines will show Pixel Depth: 30-Bit Color (ARGB2101010) or Pixel Depth: CGSThirtyBitColor. I have also been able to get 30-Bit color working on my Dell U2713H via DisplayPort. Support seemed sparse and intermittent in earlier versions, but as of 10.11.3 everything works well in my experience.
The apple website notes these LG panels are P3 color gamut compliant. Which is a smaller color space than Adobe RGB, but probably sufficient for 10bit per channel. While the OS has supported 10 bit since a recent update to El Capitan, there are almost no Mac applications that make use of this. Unlike on Windows, where 10 bit color support and display panels have been available for several years. And note, the latest MacBook Pro panel still doesn't support real 10 bit. And if you want to use wide color with a secondary panel, you'll need to buy a laptop with a secondary GPU.
On the PC side, it's much easier to get the right hardware and get Adobe tools to display a wide color space. Apple is still far behind on what has become absolutely necessary for photographers and filmmakers.