I think it's interesting that they do this in the UK. The UK has a bit of a history when it comes to financial innovations. E.g. the first national bank was created there, it's still a major financial center, and it's a country that is very dependent on international trade and literally built the foundations of the modern financial system in the seventeenth century at the same time they took over management of their huge empire. It's no coincidence that those two things happened at the same time. Their new financial system funneled huge amounts of trade through London, which in turn allowed it to go out and conquer the world. Basically they scaled trade by de-risking it. Before banks, you had to move gold around which was slow and exposed you to robbers. After banks happened, you had messengers transferring bills to each other. The Spanish were still shipping (and occasionally losing) tons of silver across the Atlantic at the time and that was their whole premise for their empire.
The UK recently removed themselves from the EU so they are once more in a position where they can play host to new financial instruments and potentially benefit from that. Crypto currencies have the potential to be very disruptive to the modern financial system. Not the worst move for them to allow some experiments to happen in their jurisdiction. If something like this takes off, it has the potential to capture quite a bit of value. If it doesn't work out, it's easy enough to get rid of it.
It's also interesting that particular block chain is based in San Francisco. The SEC is allowing this to happen, apparently (probably for the same opportunistic reasons the British allow this). These MobileCoin guys are well funded apparently and not by means of an ICO but by good old VC cash. VCs are smelling money, that's why this stuff is happening and why the SEC is being a bit hands off here. There are quite a few block chain companies operating in the US actually. There already is quite a bit of VC money locked up in that.
It's also an interesting counter move to Facebook's Libra as well and kind of embarrassing for them that particularly Signal is doing this given that it is backed by one of their former Whatsapp founders. Libra in turn was a counter move to Telegram's plans (yet to materialize) and inspired by China's WeChat.