The trust dynamic is the opposite of what you think - SGX doesn't enable an enclave that protects the machine owner from the code they execute; it enables an enclave that protects executed code from the machine owner.
The largest consumer application of this is DRM - modern UHD Blu-Ray playback on a PC requires a fully SGX-enabled backend; the negotiation to obtain playback keys and the decryption of the on-disc content is done in the SGX enclave.
In that case the DRM code running in your PC is in a hostile environment. That is someone else's code running on my host and fearing me. The dynamic is exactly as I described. The question is: Whose code are you going to run on your machine? And why is there a trust issue?
We've already seen the Sony rootkit fiasco, so it doesn't seem unfair to say one should not trust what DRM providers are doing. We should definitely not let their malicious garbage run in a secure onclave where you can't tell what it's doing as suggested by these researchers.
The largest consumer application of this is DRM - modern UHD Blu-Ray playback on a PC requires a fully SGX-enabled backend; the negotiation to obtain playback keys and the decryption of the on-disc content is done in the SGX enclave.