I checked, but didn't see anyone with this found. If it was and I'm just blind, feel free to lock or delete the thread. With the advent of flying in the Shadowlands, Blizzard's flaws in the terrain are more easily found. So far, I've only found one in Maldraxxus. Over by the Theater of Pain, to Unbreakable Urtz' left, is a hole in the mountain attached to the Theater. You can see the opening here:
It's kind of hard to spot from a distance. Here's a closer look at the spot.
And one more, showing you the inside of Maldraxxus' landscape:
There's a pretty hefty amount of disconnecting that you'll do if you go too far down. I ended up getting disconnected about 22 times before getting annoyed, but I just have a short temper. I flew around the entire zone looking for other entrances, but this is the only one I managed to find. Perhaps more experienced explorers will be able to find neat stuff with this.