While people still have old handsets and those handsets are in demand there will always be updates thanks to ROMs. Of course older handsets are not officially supported developers have a lot of love for them and this has been proven as Android 7 Nougat is heading to the Samsung Galaxy S3.
The Nougat update for the Samsung Galaxy S3 is coming from CyanogenMod CM14 and owners can install it just as they would with any other custom ROM by flashing.
Many owners of the Samsung Galaxy S3 are used to flashing ROMs onto their handset as in the past there has been custom versions of Lollipop and Marshmallow. To flash the ROM you are going to need to have CWM or TWRP installed, but if you already flashed a ROM to the device you will have one of these.
To go ahead and put Android 7 Nougat onto your Samsung Galaxy S3 you can follow the steps in the video which you can find below. At the moment the ROM is still in the early stages so there may be some issues.