Soeheil bunq offers much more than just savings accounts. A reference account would protect only one part of customers, and it's unclear to me how much of a security win this would actually be even for customers that deposit only their savings at bunq.
After all, if people go as far as installing software like Anydesk just because someone told them to (no offense to the victims, but objectively this is what happens), then the fraudster could probably also get away with making further adjustments to the bunq account of the victim to have the reference account changed.
And while you could argue that bunq should just not let the user change the reference account, what happens if the reference account at the other bank gets closed? This might not even solely be the user's fault, as every bank is just a company and can decide to terminate their customer relationship for several reasons. If something like that coincides with an event in the user's life where they need to withdraw money from their savings account without lengthy wait times, then they wouldn't be able to do so.
Ultimately, bunq itself has more background info on the situation of course, so it might be they'll come to the conclusion that there is enough of a security advantage to a reference account option to render these contra points nil. But as far as I personally can see, it's not completely black and white. Especially because with bunq you can be very sure that they will never call you and that all important communication is made solely through the bunq app, nowhere else. That being said, in many years as a bunq customer I have never received any phishing whatsoever, be it through SMS text or email. If there is someone out there leaking data, it's probably nothing to do with bunq themselves.
