The short and sweet of it is that Gran Turismo 5
looks like it'll be getting a track editor
but the time frame is unknown at this point. That's a long overdue feature in my opinion and I'm happy to see it coming. I have a lot of friends who are big fans of the series and I'm sure this news will make them pretty happy. Plus it will help prolong the life of the game as you'll be able to play many more tracks than what comes out of the box.