As it happens, we're not sure how reliable our source is, so take with a big fat pinch of salt.
E4G have "confirmed" this weekend that Gran Turismo 5 will launch with a track editor. According to them you'll be able to edit or build your own tracks for the game, presumably for sharing online. It would certainly give you more chance to use those 900 or so cars with an infinite pool of tracks to choose from right?
Apparently SCEA confirmed to E4G, Yes it will have a track editor. You will be able to rebuild a track from scratch or edit the tracks that are already put in Gran Turismo 5.
We're not sure what to think about these rumours to be honest. It's certainly within the realm of possibility, but we're questioning ourselves how likely it would be.