This is quite a long thread, so forgive me for not reading it all and that someone has already posted what I'm about to do.
For me this means that all development is done, or rather, PD is done puting everything into the game they decided to do. And also, all the major known bugs are solved. Maybe a few minor ones remain, but their chance of occurance is either very small, or the impact for the player is very small (or both). With GT Mobile being done too, the development team has time to spare (maybe even bored).
So this leaves them time for puting in some extra content, content they hadn't thought of yet (hence their visit to the Forza stand at the E3 for inspiration) or content they just hadn't scoped yet for GT5, but intended to give us anyway as DLC or in GT6+.
It all depends on Sony's release plans for GT5 and the impact any additional content has on development and testing. Quick wins with low risk can be put in. Quick, low risk, wins could be finding additional ingame sponsors (track sponsor boards, car stickers etc.), track enhancements (more detail such as oil drums, cars, debris or anything else that is not animated), music, skies and
skylines, etc.
I can't think of any higher risk content, simply because it is unknown what they have already put in. If PD goes for additional high risk content, than it will still have to be something that can be made within a few months, anything taking more time will be plain silly. Enough is enough.
Just a few thoughts.