I got the answer I was looking for from reddit but I will post it here as well so it my help somebody in the future:
There is "only"
2**256 different storage locations possible. By creating an array that uses almost
2**256 words of storage, it is almost certain that any variable you create would actually conflict with that array. Of course, in reality, the chance of collision is still incredibly low since filling an array of
2**256 words would require more computation than exists in the universe....
A variable like that is deployable on testnet but that is because you can declare "hey this storage should be set aside for the variable 'test'"... but until you actually do something with it, it won't cost any gas. If you tried to iterate through the array, that's when you'd hit out of gas exceptions.