Let's posit that Sony (or another company) is in the consortium holding the TPM root key. They will then be able to install a truly undetectable and unremovable

Let's posit that Sony (or another company) is in the consortium holding the TPM root key. They will then be able to install a truly undetectable and unremovable you-name-it. You are quite correct in implying that a TPM would prevent a repetition of the Sony scandal. It would do this simply by preventing discovery. Of course, it is also possible that Sony in particular would not be given access to the magic key. They may have to pay a steep tribute to, say, Microsoft, to slip the payload through. Whether currently sold TPM chipsets are capable of such feats is immaterial. The camel's nose is in the tent.