Tell that to the sisters of battle. All but unmentioned from rogue traders release to very late second edition.
Tell that to the C'tan, who appear at the head of the necron army, despite only having been mention once years before, and so on...
Gnomes might still be canon, but simply not have come up. Do i really want that to be the case, not really, they don't fit well with my vision of the warhammer world, but there has never been a book that deals in detail with the area where the gnomes are reported to live, that has failed to mention them. We haven't had a suppliment that talks about Ind in a while, but i'm pretty sure it still exists in the warhammer world.