Ultimately, that promise from 2013 hasn't come true. The "GPS data grabber" is only useful for watching "virtual replays" of your exploits on tracks that are already mapped in Gran Turismo 6 "stock".
But the "Track Editor" has finally arrived. It's taken the form of an app for iPad and Android tablets, where you can create a track quite intuitively (we've tried our hand at it, and the result is acceptable). So if you're tired of the official tracks (which are not few) now you can propose to create virtual circuits that, in addition, you can use in online mode games with your friends.