What is different?
GUI 1.* uses an icon font where each icon is a character in the font. Although this works well, there are a couple of drawbacks, including accessibility and file size. Using the new icon system, we can now display semantic, accessible icons when required.
Icons as background image
In certain cases where an icon does not add direct value, you may not want a screen reader to detect the icon. In these instances, you still have the option to use the icon as a background image. Doing so will mean that the image will not be read out by assistive technologies, nor will it easily print.