As I pointed out elsewhere in the thread, Signal uses SGX to let clients confirm exactly what version of the contact discovery server software they're running against:

https://signal.org/blog/private-contact-discovery/

It's not bulletproof by any means (https://signal.org/blog/private-contact-discovery/ goes into this, and also points out several features they've used SGX for since), but it's certainly something, and they're doing it.