After looking around. I found some youtube links that show there is a chest hidden in the same way as the borderlands 1 chest.
In the map Tundra Express, from the fast travel point. Keep the glacier on the left, and start walking past it. You should walk directly past a varkids camp. And eventually you will reach a open cliff, with a end of map turret on the right (and a varkids camp). Drop down from the cliff to reach the chest. It is under the border turret. Be careful not to jump outside of the map.
Ps: enjoy the view, the train rushing by is nice.
The chest is however not as badass as the borderlands 1 chest. So it contains few overlevelled guns, and purple or orange rarity weapons. It does contain a bit better loot than normal in my limited experience. (I found my first non-quest relics there).
So far I do not know if it remains a good chest, or if it is the only one. And I'm not totally sure it contains uber badass loot.