I thought you was suggesting a TPM wasn't needed at all, but a TPM is needed to get quotes.
replyThat said, TPM quotes are attesting the value of TPM PCRs which are just registers of hashes (representing the state of the machine).
When making a CSR, you can use https://tpm2-tools.readthedocs.io/en/latest/man/tpm2_certify... to attest a key is TPM-resident.
I think your central thesis is that at the time of TLS establishment, why not use PKCS11 (with a cert signed by a CA that has validated a TPM certification), and I agree: services should probably integrate via PKCS11.
I just read your original comment "is this any conceptually different from using PKCS11 provider for TPM in OpenSSL?" and yes, I agree it's not conceptually different.
replySorry to have missed that!