Relic said they weren't putting in the Tyrannids, not because of the mod but the effort on their part in making it work well before they heard of the mod. They said that the platform wasn't built with flight in mind, let alone Tyrranids, they have flight, but the horde structure of Tyrannids might not fit well on the game's code as it is now. That said, DOW 2 is now rumoured to be in production, which probably will have said alien swarm.