Over on the official forums for Call of Duty: World at War, Treyarch's community manager, Josh Olin has said that not only is Map Pack 3 currently in the works for PC, but so is a patch.
Here's the post:
As with the previous two Map Packs, Map Pack 3 will indeed be coming to the PC – the team is hard at work on it and I'll let you know when it's in test.
As such, there will be a Patch 1.6 as well, which will address some additional game issues. When I have details on what else will be included in the patch I will be sure to post them.
We appreciate your patience as always, and look forward to its release as much as you do!"
Good to know.