Retina.js - What about support for 3x images?

The Retina.js script is awesome for handling the issue of displaying either a 1x or 2x image depending on whether the device is a retina display.

What about 3x? Retina.js doesn't seem to support 3x retina, so I assume most websites nowadays just display the 2x ones, even on the latest phones such as iPhone 6s?

Tks!