> In order for signal to compete in the 21st century with messaging apps around the world they need a payment story.

No, it does not.

There are two distinct groups of people using Signal. None of these groups needs MobileCoin-based payments.

Group one is probably the biggest and consists of "normal" users which use Signal because it's the free messenger that is NOT affiliated to Facebook and has a good reputation with regard to privacy and data protection. There's another messenger with similarly good reputation, Threema, but that one costs money, hence Signal is the more popular choice. These users may indeed find a simple payment solution through their messenger a useful feature, but they want to send each other "money", not "MobileCoins". Those are not interchangeable for this kind of user; they expect to send whatever is their local currency, USD or EUR or whatever, and they expect the entirety of the money they send to arrive at the target - having 20% crypto market swings within minutes eradicate 20% of their share of last week's restaurant check while they're transferring it to their friend is a non-starter for this group. So are exchange fees for USD-MOB/EUR-MOB exchanges before and after sending money, even if the exchange execution itself may be automatically run in the background. This is true especially since there are already well-known and established solutions out there specifically targeting this particular need - PayPal Friends and the Cash App for example. Sure, it would be nice to have messenger integration, but if the only way to get that is to transact in MOB instead of USD and always send 10% more value than you intend to pay just to ensure the receiver gets "enough", the established out-of-band solutions which don't have those problems will simply be used. Also, this group doesn't really have strict anonymity requirements, because they usually send money (and messages) to people they know in real life as well. Whether your awesome crypto coin is more anonymous than PayPal thus doesn't matter at all for these guys.

Group two consists of those that actually depend on Signal's security, privacy and anonymity features because they need exactly that in a messenger. Think whistleblowers, journalists, people doing stuff that's illegal where they live. A lot of these want to send information to their contacts, not monetary value, and don't have any use for a payment option in a messenger. And even those that do want to transfer monetary value won't exactly be enticed by a one-click crypto transfer feature in their secure messenger, since they can be assumed to be technically competent enough to utilize the already-existing cryptocurrencies (especially those with a much longer history of privacy protection, such as Monero) and crypto exchanges to perform whatever monetary exchange they want to do. I would even say that these people would explicitly NOT want to use a messenger-integrated cryptocurrency, because that limits them in their choice of cryptocurrency and fiat on/off-ramps, which are crucial decisions to be made carefully if you want to preserve your anonymity. And the entire idea that these guys would switch from Signal to WeChat just because "WeChat has a money sending function" is blatantly absurd.

I do not see any sufficiently large group of people that might get any value out of this MobileCoin-Signal-integration feature. Hence I predict this feature to ultimately fail due to lack of user interest. But that will only become clear AFTER a lot of good-will from tech- and privacy-minded people has been burnt by this unnecessary stunt, as can be seen for example here in the HN comments.