SDC has more than enough land at it's immediate disposal to do what they want for the foreseeable future. They might continue the loop around the lake someday, but they aren't going to expand the park indefinitely like some sort of roller coaster tycoon park. As far as coasters go, there's plenty of room to run them back into the land that SDC owns around the perimeters of the park. There are some issues with caves, especially on the southeast corner, but I don't think they'll ever have too much trouble fitting in new stuff.