I can't say that this interests me massively. I'd like to see something more realistic rather than just another arena twitch shooter.
I can't see how they're going to balance it realistically and keep the fluff. The SM are already too fast and too squishy, so how are they going to realistically introduce Eldar and keep them feeling like Eldar? They'll all be getting one-shotted. Orks? They'll never even get into range unless they're made extra tough.
They should introduce guardsmen, but rather than control just one, you have your main character and 2 squadmates (controllable pets) Get three of you together and you have 9 guardsmen! That's more realistic.
But personally, I'd prefer something a little slower paced and tactical, rather than just run in blasting everything.
Imagine if they made a more strategic game, like ARMA with 40k (I know they've made a mod, but it's terrible)
Now watch this video and imagine guardsmen or SM.