they are saying that this game will be more of a mix of FPS than RPG, however they have made it clear that this game is first and for most an RPG... it is rather confusing as in how exactly that works, but that is their statement on the matter.
mechanics like shooting, taking cover, sniping, laying down supressive fire with heavy bolters and the such will be in the game which make it sound like an FPS, but stating that it is an RPG (thinking dice rolls) i'm not sure how it world work
as for the factions
all 7 faction seen in the table top will be seen, but it is more than likely only a handful will be playable. more than likely you'll be only able to play as space marines, eldar, chaos space marines, and maybe tau. every other race will be relegated to being an NPC fodder unit.
to me, i don't think this will be very successful, this game is supposed to be a squad based shooter on epic scale... not a grindtastic rpg.
if they made this an MMOFPS with RPG elements with the worlds populated by NPC hoards then it would be epic and i would play it forever. but if they make it like a WoW clone in a shallow attempt to jump into the MMO money wagon i will be sevearly disappointed.
the only thing that would make me buy this game is if i could be a Khorne Bezerker. any chance i can spill blood for the blood god, i take it. it is why i disliked the warhammer mmo, tzeentch? What about the blood god!? why can't i be a devotee to khorne dammet!?