It is so cool to see so many new ideas for Monzo cards! Thanks a lot for taking the time to do it 
To give a bit of an update, we’ve only recently started to work on what a new design system for what our cards should look like. Things like our future business banking will require new cards so we’re working on something that would allow us to create new “kinds” of cards in a sustainable and consistent way and without breaking any of the things that make our current cards great.
We’ll be sharing updates soon but I can tell you we’re looking into pretty much every aspect of what makes a card a card. Colours and inks, materials, finishes, magnetic stripes and signature boxes, embossing techniques (now that we have Google and Apple Pay it’s not that important to make the card camera-friendly), questioning what information we need printed on the card and what we don’t, etc.
We’re literally looking at every option to go and make our cards even better (not different, but better). Stay tuned 