Martijn I will copy-paste @John Do's answer from the thread where your post comes from;
I quote @Ali "We looked at the metal passes a long time ago and decided not to do so. This is because the passes are so incredibly environmentally unfriendly that they do not suit us well. Moreover, there is still some hindrance in daily use (breakage, scratching, etc)." (original post was in Dutch).
Reference: https://together.bunq.com/d/4446-second-design-card-option-metal/4
I don't think bunq will/should spend much time on this. After changing card suppliers a while back the cards quality improved in my experience. I remember Ali taking one of my more recent cards and just scratching like crazy on them with sharp objects, but the print didn't really seem to care about that. Now, that was just a quick test-run of course, but I believe the cards already got a lot better (further improvement might be possible). As for the metal cards, sorry, but that's really just a gimmick to me. 🤷♂️ I would rather like the sparse resources being spend on things that improve the product experience (a different card material won't change anything in terms of functionality). Just my 2 cents. 🙂
PS: Your mockup looks amazing btw. 👌