You can't even use MobileCoin in the US (Not that I'm a Signal user) but are they either planning on focusing on foreign markets, or planning on getting audited heavily by all the US financial agencies?
> The first payments protocol we’ve added support for is a privacy focused payments network called MobileCoin, which has its own currency, MOB.
(Emphasis mine.)
[0] https://signal.org/blog/help-us-test-payments-in-signal/