Not a very surprising choice given Signals current use of SGX and reliance on their centralised server. It's a bit of a shame as MobileCoin doesn't offer as strong guarentees as other privacy coins but I'm interested to see how they maintain privacy whilst peg the transacted value - I can't imagine how they wouldn't have to rely on an exchange for liquidity.
SCRT network is a similar project that uses SGX but supports smart contacts so they could have a Maker like pegged token.