Ahh, wrote this reply out yesterday but forgot to press send 
We have got some initial designs that we’ve done some testing with, though they’re not in any build yet. For now we’re focusing on the current account but fingers crossed it’s something we can get in the app within a few months.
In terms of the UI, we really see it as an extension of how send and request works, though the main difference in cost sharing/bill splitting is that the payment will be attached to a transaction. Here’s a quick sneak peek: 
This design is definitely liable to change and still has some way to go before it sees light, but hopefully everyone can now get a feel for what we may do 