It says Wrath of the Lich King because it was during the WLK presentation they went over the Catacombs and why they never implemented it.
It is highly, highly unlikely that the catacombs will EVER be implemented in any similarity to their internal death-match development. Content like this gets developed and scrapped all the time, so just because they have this partial map layout and had at one time a system for how the battleground would play out doesn't mean there is any inclination to actually release it.
Some things just get phased out as WoW progresses. The Gurubashi arena is probably one of those things.