Is this making confidential computing obsolete?
Credit/debit cards with chips (EMV) are another proof of existence that hardware-based protection can exist.
> It is not evident that there even is a way to implement the kind of guarantees confidential computing is trying to offer using hardware-based protection only.
Not in the absolute, but in the more than $10 mil required to break it (atomic microscopes to extract keys from CPU gates, ...), and that to break a single specific device, not the whole class.
And the key would not allow you to jailbrake another Xbox.
So at most you might be able to make a PC look like an Xbox, but a PC is more expensive to start with.
So unclear exactly what you have accomplished.