A mob area dedicated to nether monsters would be great! Except, there wouldn't be pig zombies unless they are re-enabled. Perhaps enable pigzombie spawning, but prevent /spawner pigzombie?
50% Support, I would like an area for nether mobs, but I think that people could farm some of the things that they drop (Iron, Gold)
Well... zombies are kind of the only ones around "littering" the floor with iron ingots. Otherwise, agreed.