It clearly wasn't an afterthought, I don't think anyone familiar with the design could possibly say that. It's intended to allow any arbitrary OS to use it, and in fact support on Linux has always been better than on Windows, largely because Intel could and did implement support for themselves. It pays a heavy price for this compared with the simpler and more obvious (and older) chain-of-trust approach that games consoles and phones use.
The whitelisting was annoying but gone now. The justification was (iirc) a mix of commercial imperatives and fear that people would use it to make un-reversable ransomware/malware. SGX was never really a great fit for copy protection because content vendors weren't willing to sell their content only to people with the latest Intel CPUs.
The whitelisting was annoying but gone now. The justification was (iirc) a mix of commercial imperatives and fear that people would use it to make un-reversable ransomware/malware. SGX was never really a great fit for copy protection because content vendors weren't willing to sell their content only to people with the latest Intel CPUs.