I think that when Cryptic decided to base the game in the year 2409, they did it with the understanding that they would have to map very large areas of space.
By the Nemesis time period, Voyager had arrived back from the Delta Quadrant with all of that information and we know from the Pathfinder Project that Starfleet was planning to send a group of ships into the Delta Quadrant, primarily to rendevous with Voyager, but secondarily to explore. I dont think they would drop these plans just because Voyager got home.
The Dominion War is over and from the various books we learned that the Dominion were going to allow ships back into the Gamma Quadrant to explore, so in 2409 there is no reason why VAST areas of space around the wormhole wouldnt have have been explored, and in fact, I would be disappointed if there wernt some races from the Gamma Quadrant that have joined the Federation by this point.
At the very least, the area around the gamma quadrant side of the wormhole should be built up Federation Territory.
So i believe that the Gamma Quadrant AND Delta Quadrant should be in at launch, not out of demand but out of canon requirement.
Expansion Packs you ask? They should be other Galaxies completely.