I have been looking at how to do cheap ($20-50 slow USB connected (essentially smartcard), $500-1000 PCIe) HSMs. If you do shared-computation with a host (with or without SGX/TXT), you can get pretty decent performance with quite modest HSM hardware.
Those provide NSA-type protection -- in that attacking a single instance isn't guaranteed, and takes time, so a system with key rotation or k of n split across locations is going to provide pretty reasonable security.
Private Core is definitely the most interesting TXT-based solution today; if you built an IaaS provider with that tech plus live video monitoring, alarms, etc., you could probably offer quite reasonable security assurances to people. (i.e. the tools to defeat it require physical access, and if no one can gain physical access to a rack once the rack is put into production...)
I agree that if you're paranoid about the NSA it probably doesn't make too much sense to have faith in the Intel PKI. When you say pretty decent performance for your HSM, do you mean less than 10 % for real world apps?
I'm currently assuming a threat model where an attacker doesn't have physical access however, and looking more into how to use hardware to bootstrap a minimal TCB that doesn't require OS or application rewrites but still gives good performance. Even if only for specific use cases.
Not sure if any IaaS providers are offering services based on it yet, though.
Then, the ability to secure those boxes (and boxes you drop off in colo) against tampering short of powering them off.
(tech details: Intel TXT, TCG TPM, cheap HSMs, Intel SGX, etc.)