So I know the idea of charities has been talked about before with things like rounding up spending to donate to charities (which btw I noticed Tesco self checkouts were trying out yesterday).
So here is my thought… A lot of businesses have a charity partner of the year or something e.g. Tesco: diabetes uk, wetherspoons: clic sargent (both worthy causes), M&S even gives you choices when you use its Sparks card.
If Monzo were ever to get one itself (not necessarily roundups), maybe an in-app vote either once out of a few options (with the most popular being the chosen charity) OR like the supermarkets are all doing a virtual charity choice token every time you make a transaction.
Another clever idea along these lines could be regional charities (because monzo has locational data about transactions) so smaller more local charities might be able to benefit.
A long way off I know (get the current account working) but just my thinking outside the box