
A developer and senior member on XDA Developers Forum, who goes by the name biktor_gj, has been able to successfully install and boot full-fledged variant of Android Lollipop operating system on the Gear S. The process involved rooting, installing custom recovery (TWRP) as well as custom kernel, and then installing CyanogenMod 12.1 on the device. As you can see in the images below, the device is running Android 5.1.1 Lollipop on that gorgeous curved Super AMOLED display.
If you are thinking of installing it on your Gear S, know that it currently only works on unlocked GSM variants of the Gear S. Apparently, the variant of the Gear S that AT&T sells has a locked bootloader, so that developer hasn't been able to find a solution to install Android on it. Hit the source link if you want to know more details about the process or development progress.