They found an area in the wilderness world rather like the emerald islands, where many diamond ores had spawned in along the ground and such. However it isn't meant to spawn because of how overly advantaged it is for someone to just claim the land, mine it all up, then unclaim it and get a quick profit off it.
It's part of the custom biomes that the server uses, however they weren't actually supposed to be used unlike the other biomes that we had. Therefore the admins have to remove the ores, just like when they had to remove all the emerald ores that were along the custom emerald islands.
I'm not entirely sure what's taking so long for this one, but I presume that Fatnoob is using the downtime to perhaps update a few things or something that needed it. Since updating things requires the server to go down for maintenance it would be perfect timing. I suppose we'll find out when it's all finished.