4.0 was released a year and a half ago, and new releases come out approximately every 2 months.

Ever since 3.0 came out, the numbering scheme has simply been "Increment the minor number every release. Increment the major one whenever we feel like it."

There's plenty of other distros out there that aren't either of the options given.

I use Arch Linux on my main machine, and Alpine Linux on a variety of other computers.

I feel like it'd be a better idea to put this in the devices that are actually playing the audio. Rather than put it in a pair of headphones, build it in as part of Android, iOS, Tizen, FireOS, and whatever else the devices are running these days. That way we can have this awesome safety feature with ANY headphones.

Main PC: Lenovo Y700 (i7-6700HQ, 8GiB DDR4 2133MHz, 256GiBSM951 SSD, 1TiB HDD)
OS: Arch Linux
Environment: XFCE4, Numix theme with numix-circle icons. Taskbar on top. Docky on bottom.
Editor: Sublime Text 3 Dev (registered). Nano on command line.
Browser: Google Chrome.
Email: Claws mail.
I run Virtualbox on this with a number of different versions of Windows, Linux, and Haiku.

Secondary PC: Toshiba Libretto 110ct (Pentium MMX 233MHz, 64Mb EDO RAM, 4.3GiB HDD)
OS: Alpine Linux
Environment: Command line / Openbox / Windowmaker (I switch as I see fit)
Editor: Nano
Browser: Suckless Surf, Dillo
This machine is used for development and testing, and as proof that modern tasks can be reasonably achieved with ancient hardware.