Nougat won't be coming the G3 as far as I can tell. The phone is over 18-months old, so Marshmallow was the last official Android release we'll see. We'll probably still get security OTAs for it, but if you want Nougat, you'll have to find a non-stock-based ROM version that is based off of AOSP (like the previous poster posted to).
Remember, since these are NOT stock-based ROMs, you will not have access to the original camera app for the G3, which means HD pictures and videos will not be possible since that is LG-specific code that is only accessible from stock-based ROM as the source code for the HD pictures and videos are not available.