It's just been a case of "to much stuff and not enough time to do it."
Throughout September and October Battleground has had a LOT going on, especially on the weekends. Unfortunately, the side effect of this is that it hasn't left us a lot of time to organize and design the league and map that will go with it.
Maybe the largest issue is the map itself. The amount of time and effort that went into the Fantasy map was... well... quite a bit. The 40k map probably has to be bigger, better designed, and done at least as well as the Fantasy version. It takes a ton of time and requires someone with that amount of time to spend and the required level of skill to make happen.... you know?
Due to this, I am very sad to report that I do not think the 40k league is likely to happen this year. This is due to several really good reasons that are very likely to benefit everyone greatly down the stretch.