What, like the Dark Eldar, the race with no background and worse sales?
The WD codex is (in the generic form) never going to permanently replace or supplant the full-up codex, even for less popular stuff. Although there are hints that GW are gearing up to start regularly putting new units for published books into WD again, dont bet on that stuff never getting into an actual book. I fully expect that when there's a spare moment in the schedule the SoB will get a fully independent codex of their own, and a significant re-launch...