HUDs are certainly not new to cars. After all, General Motors has championed the technology since the '90s in many models, but technological breakthroughs are making them more common. According to Automotive News, in 2014, there are 38 vehicles on sale in the US with standard or optional displays, up from 13 in 2009.
The technology works with an optics box projecting an image on a specially coated windshield in front of the driver. The breakthrough has been shrinking the box while making the image larger and more colorful without operating too hot. Panasonic unveiled a unit half the size of competitors at the 2014 Detroit Auto Show that displayed a 6-inch high and 16-inch wide image, twice as big as others.
There is a second, cheaper solution too. These so-called "combiner" HUDs project the image on small transparent panes. This is the solution that Mini and Mazda are using. While less expensive and more compact, they have lower image quality than traditional displays. Automotive News cites an IHS forecast that HUDs will be found in 9.1 million cars worldwide by 2020, up from 500,000 this year, and most of them will be combiner displays.
Given the technology's relative simplicity, it's amazing that it has taken so long for head-up displays to make it to cheaper cars, but it seems that its time as come.