Originally Posted by Elden
there are 3 locations which are locked even once you finish the game (they are a the far left side of the historia crux when is not in the toogle view) This locations are for valhalla, serendepity and coliseum ... i guess you can unlock theme by buying theme? Am i right?
Well I have the preorder bonus DLC and the middle of those three far left locations is in fact the Coliseum where you can battle Omega, Lightning etc. The other two are still grey for me though and I have all 160 fragments and have seen the secret ending so who knows, future DLC. Wouldn't mind having confirmation on those two myself.
So I think you can only open one by buying the DLC.
The new part of the casino being developed is most likely DLC, we already know at the end of this month there is a Sazh DLC based in Serendipity so that will likely answer your question about why you saw Sazh there in a gate window and why they say they will be opening a new area soon.
As for your first question, we can only assume that we will get a true ending through DLC. It's been denied that there will be a XIII-3 but to be honest, I take anything Square Enix says with a pinch of salt these days. They have confirmed they will be extending the game with DLC though so it's a possibility.
Oh and I doubt they will put a time frame on when you can buy DLC, no game has done this in the past that I know of, it would be foolish to prevent yourself from gaining more money by taking it away when someone might like to purchase it later, right?
Hope that helps~
This probably could have been squished in with the XIII-2 Endings Discussion topic by the way buddy. :]