Is the dwarf faction done? If so you should include it into the game.
Companies should stop doing this type of thing. You should go above and beyond on the first release. Who wants to spend $30 dollars on an expansion that adds two races and thats it? Not saying thats what you'll do, but we're starting to see it alot in the rts community, and soulstorm/kane's wrath were both **** poor expansions for what they cost.