Apple Glasses. They're fun to think about, and multiple rumors suggest they might actually be in development.

But they're probably not coming anytime soon.

According to a Friday report in the Financial Times, Apple is still experimenting with multiple different prototypes of augmented-reality glasses -- including some where you might have to wear your iPhone on your head.

While the goal (according to the report) is to "move cameras, sensors and screens from the smartphone to the face," the Times reports at least one of the prototypes would use the iPhone as its primary screen.

(How are people supposed to see through an iPhone, you ask? Check out this iPhone-based AR headset.)

More importantly: if several different groups of engineers are still experimenting with several different prototypes, it's not likely we'll see one of them on shelves anytime soon.

But it does seem likely that Apple's working on such a thing, seeing how it purchased a company that specializes in eye-tracking, and how Gizmodo discovered an incident report where Apple employees complained of eye pain after trying an unspecified prototype. Bloomberg reported that Apple was mulling smart glasses in late 2016. A few months later, tech evangelist Robert Scoble wrote that Apple was working with optics manufacturer Carl Zeiss.

Facebook has confirmed it's working on AR glasses, but warned that they will take a while.

With or without glasses, Apple's new ARKit platform is already giving the company a foothold in the augmented-reality race. Research firm IDC said today it expects spending on virtual and augmented reality to double each year through 2021 -- at which point it could be a $215 billion industry.

Apple didn't immediately reply to a request for comment.

Here's what it's like to play Super Mario in AR.