Not as a race, no. But as a special NPC-event, yeah, it could be pretty cool. Imagine - a fortress on a continent is about to fall. It's the third in the past week - Chaos has been marching on all Imperial Territory and kicking ass due to a recent influx of players. The Marine players are resigned to their fate, and are about to start pulling out again to defend another fallback fortress, when some of the frontline squads report strange occurrences. Ethereal Marines, clad in black power armor with bones visible through those blessed plates eerily and teeth chattering, are appearing on the battlefield! The Chaos forces are routed, and the Marines are saved. Of course, it wouldn't happen a lot, it'd be very rare, in fact. But as a randomly occurring event, it could be totally awesome.
Actually, could be some kind of resource Space Marine forces could use during the heat of battle. Much like the Tyranids are NPC controlled, so too could be the Legion. Called upon at GREAT resource cost or something of it's ilk, they appear and assist a beleaguered Space Marine force should it be overwhelmed. Could almost have it be random what shows up, maybe other Chapter forces or what have you with the Legion showing up being something uber rare and slightly more powerful then the regular usage. Could have something like this for every faction.
guys come on... the game has barely the basics down... we basicly know nothing... all we know is that tyranids are gonna be NPC faction... its is a liiittle too early to go into very specific NPC stuff for any faction... besides... the imperium doesnt even officially know they exist... besides they would come storming into a battle full of other space marines... the lore suggests that they show up mostly with the imperial guard and when they do most of the guard is dead anyways so no one can officially confirm anything... they are a mystery and needs stay that way... maybe there is a place for them in some future patch or we can find clues on a space hulk or whatever but for a pre beta/ pre launch thing... no just no... as for "reinforcement" it is far more likely to just use imperial guard!
So, what you're really trying to say is, don't speculate because we know nothing concrete? Isn't half the fun speculating about a game before it's launched? Not that everything has to be true but at times it gives the devs or other people great ideas directly or inadvertently. It's not early for anything, let alone fun speculation. It doesn't really matter how far fetched.
you can do what ever you want... im just saying hyping yourself will only get you dissappointed... besides why would developers even consider this when they have to get the very basics down first? do you even know anything about making a video game?
