Also, all the user added content they say will be avaialble makes for high replay value

What do you mean by "sandbox mode"?  Do you refer to "skirmish" or "quick battle" where you set up pre-conditions against the AI/other players?  I've just never heard of "sandbox" used in conjunction with a TBS or RTS.

Will there be a way to implement kind of triggered events? And to change the victory conditions through scripting?

How would a story in a sandbox mode even work. You have a randomly generated map, and though you could create a randomly generated story, sounds like a lot of work that would lead to some pretty meaningless, probably even weird, stories.  I would think scenarios would be more of what you have in mind and maybe parts of those can have random elements.

The sand box mode will have tons of story in it because there are quests and such triggered by player actions.

Awesome! Plus the modding options will also provide lots of gameplay fun I'm sure!

Think like any of the Civilization games.  You choose some parameters for the game such as map type, number of AI, difficulty level, how fast tech goes, is trading allowed, etc. and then the game randomly generates a game/map based on your choices.

Frogboy mentions quests and I take this to be a more advanced version of the quest/random event system found in Civ 4.  In that you might get the "Master Blacksmith" quest in which you must build X number of forges in a certain amount of time and if you do it before anyone else does then you get a certain bonus and you might get a choice of bonus' depending on other part of your empire like if you have adopted a religion or if you own a certain great wonder.