That private key can be a 'dead'* key, correct? So if you wanted to have 'Code is Law' style contracts which can't be modified by anyone, you could do that. You could even take a contract which has matured over the years, duplicate it with a dead key and be confident both that it's a well tested and understood contract, and that nobody can usurp it in any way.

* provably unowned, like 0x111111... or whatever the format is in EOS