There's hardly any doubt in my mind that Darkhorse will eventually release this. As others said they released both Japan and King of Wolves and they release a lot of less popular works by other artist with bigger selling series they have license too. Some other examples would be the author of Triguns other series Blood Blockade Battle Front and Hellsings author's Drifter. Hell, they even released two books of short stories from the creator of Eden, a series which actually sold very poorly.
So it might be a while, but we'll get it, considering Berserks popularity.