More of a niche request, but hopefully an easy one :-).
For users with UK and US (or any future Monzo locale offering) it would be cool to be able to transfer money between accounts as easy as same locale accounts. This is already pretty easy with the transferwise integration, but, could be even simpler no need to right down us/UK account numbers in the transferwise prompts, the app already has access to all the data it needs.
New feature, I dub the, Hassle free international transfers.
-Joe