A patent alone doesn't really mean they've been actively working on it for that long. It's very common for companies to register patents for things they don't plan to produce (either ever, or until some future point.)

If you read this patent, it explicitly says that it's a continuation of an application that was granted as 9,965,157. If you look at '157, you can see that it was granted in May 2018. It has the same line drawing of the headset and the same quotes on how it could be used. 9to5Mac somehow missed this five years ago. The corresponding published application, 2014/0129938, was made public in 2014, with the same drawing and example uses. Actually, we can go back to the 2008 published application 2008/0276178, with the same drawing and examples.

Just to make it clear, this isn't a new revelation at all. These were all public patent applications going back at least 15 years. Patently Apple first noticed it in 2014, so they were only six years late.

Edit: Electronista was first to notice in 2008, the same day it was initially published , picked up by The Unofficial Apple Weblog later that day and then by MacRumors a day later.

And this is what they came up with?