PlanetSide 2, at least initially, will be set on Auraxis (the original setting of the first game.) It is not yet known whether this means that the original continents will return. Long term plans are to eventually expand to more Planets.
What is known is that there are no sanctuaries. Instead, it seems each faction will have a protected area on each continent from which they can launch operations.
The engine is capable of weather effects, however they are not sure whether this will make it in for launch. Day/Night cycles have been confirmed, however.