Signal users should be happy about this, because it exposes the SGX enclaves as the false security it is. It's not like this is the first SGX exploit.
You should assume that Signal engineers, if they chose to, could access the user data protected by SGX, just like they could log metadata about your message sending and receiving patterns. You only have their word that they don't. The NSA could certainly bypass the SGX given access to the server.
I suppose there may be some legal benefit in putting the data "out of reach" - it would be hard to prove in court that you were capable of leveraging an exploit towards SGX to provide the requested data. But NSA/others will happily take possession of the hardware and do it themselves.
You should assume that Signal engineers, if they chose to, could access the user data protected by SGX, just like they could log metadata about your message sending and receiving patterns. You only have their word that they don't. The NSA could certainly bypass the SGX given access to the server.
I suppose there may be some legal benefit in putting the data "out of reach" - it would be hard to prove in court that you were capable of leveraging an exploit towards SGX to provide the requested data. But NSA/others will happily take possession of the hardware and do it themselves.